Coherent acoustic phonons in YBa2Cu3O7/La1/3Ca2/3MnO3 superlatticesWei Li, Bin He, Chunfeng Zhang, Shenghua Liu, Xiaoran Liu, S. Middey, J. Chakhalian, Xiaoyong Wang, andMin Xiao Citation: Applied Physics Letters 108, 132601 (2016); doi: 10.1063/1.4945333 View online: http://dx.doi.org/10.1063/1.4945333 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/108/13?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Persistent photoconductivity in oxygen deficient YBa2Cu3O7−δ/La2/3Ca1/3MnO3−x superlattices grown bypulsed laser deposition Appl. Phys. Lett. 103, 122603 (2013); 10.1063/1.4821746 Thermoelectric properties of YBa2Cu3O7−δ–La2/3Ca1/3MnO3 superlattices Appl. Phys. Lett. 101, 131603 (2012); 10.1063/1.4754707 Antiferromagnetism at the YBa 2 Cu 3 O 7 / La 2/3 Ca 1/3 MnO 3 interface Appl. Phys. Lett. 84, 3927 (2004); 10.1063/1.1741038 Superconductivity depression in ultrathin YBa 2 Cu 3 O 7−δ layers in La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7−δsuperlattices Appl. Phys. Lett. 81, 4568 (2002); 10.1063/1.1526463 Magnetism and superconductivity in La 0.7 Ca 0.3 MnO 3 /YBa 2 Cu 3 O 7−δ superlattices J. Appl. Phys. 89, 8026 (2001); 10.1063/1.1370994
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 129.15.31.185 On: Thu, 19 May 2016
23:52:30
Coherent acoustic phonons in YBa2Cu3O7/La1/3Ca2/3MnO3 superlattices
Wei Li,1,2 Bin He,1 Chunfeng Zhang,1,a) Shenghua Liu,1 Xiaoran Liu,3 S. Middey,3
J. Chakhalian,3 Xiaoyong Wang,1 and Min Xiao1,3,b)
1National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093,China2Institute of Signal Processing and Transmission, Nanjing University of Posts and Telecommunications,Nanjing 210003, Jiangsu, China3Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
(Received 27 January 2016; accepted 22 March 2016; published online 30 March 2016)
We investigate photo-induced coherent acoustic phonons in complex oxide superlattices consisting
of high-Tc superconductor YBa2Cu3O7�x and ferromagnetic manganite La1/3Ca2/3MnO3 epitaxial
layers with broadband pump-probe spectroscopy. Two oscillatory components have been observed
in time-resolved differential reflectivity spectra. Based on the analysis, the slow oscillation mode
with a frequency sensitive to the probe wavelength is ascribed to the stimulated Brillouin scattering
due to the photon reflection by propagating train of coherent phonons. The fast oscillation mode
with a probe-wavelength-insensitive frequency is attributed to the Bragg oscillations caused by
specular phonon reflections at oxide interfaces or the electron-coupling induced modulation due to
free carrier absorption in the metallic superlattices. Our findings suggest that oxide superlattice is
an ideal system to tailor the coherent behaviors of acoustic phonons and to manipulate the thermal
and acoustic properties. VC 2016 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4945333]
Phonons are major excitations involved in heat and sound
transportation in nanostructures. By controlling phonons with
artificial periodic structures, a remarkable progress has been
made to alter thermal and acoustic properties in materials.1–11
For example, the elastic periodic structures, such as phononic
crystals12,13 (analogues of the electronic and photonic crys-
tals), can modify the phonon dispersion and form a thermal
bandgap,1 which is critical for enhanced functionality of ther-
mal and acoustic devices.14–18 Additionally, coherent phonon
behavior is a recent active subject which has been intensively
investigated in phononic crystals, resulting in a number of fas-
cinating phenomena of prominent applied significance, includ-
ing coherent phonon scattering,4 coherent thermal transport,6
and coherent phonon amplification,7 to name a few.
In a simplified view, the propagation of coherent pho-
nons in a periodic structure modulates the dielectric constant
dynamically, which can be monitored by time-resolved
pump-probe spectroscopy.7,19–24 Ultrafast optical excitation
of solids suddenly launches the forces that can excite the
coherent coupled electron and lattice oscillations. With the
propagation of coherent acoustic phonons into the sample or
the generation of coherent optical phonons with in-phase
atomic vibrations, the oscillatory behavior may be captured
in time domain by monitoring the optical reflectivity of a
probe beam.25 These oscillations originating from either light-
wave interference or phonon-wave interference can provide
wealth of insightful information on the coherent lattice
dynamic.25 Periodic structures of two-dimensional ultrathin
layers, known as superlattices, is an ideal playground to study
the physics driven by coherent phonons.4,6,7,15,26–31 Towards
this end, coherent phonons in superlattices have been exten-
sively investigated in semiconductor heterojunctions7,21,32–37
by ultrafast pump-probe spectroscopy. In contrast, their
dynamic behaviors in superlattices of oxide compounds with
strongly correlated electrons have been rarely explored.
In this letter, we report on coherent acoustic phonons in
ultra-thin complex oxide superlattices composed of epitaxial
high-Tc cuprate YBa2Cu3O7�x (YBCO) and ferromagnetic
manganite La1/3Ca2/3MnO3 (LCMO) layers. By applying
ultrafast pump-probe spectroscopy, we have identified two os-
cillatory modes in time domain: namely, the slow mode with
a clear frequency dependence on the probe wavelength which
is assigned to the stimulated Brillouin scattering by the propa-
gating coherent acoustic phonons; and the fast mode without a
dependence on the probe wavelength which is ascribed to the
photon Bragg reflections at the YBCO/LCMO interfaces or
different free carrier absorption in the metallic layers. These
attributions have been further confirmed by performing addi-
tional measurements on the superlattices with different thick-
nesses of YBCO layer.
The superlattices used in this study were grown in a
layer-by-layer mode on atomically flat single crystal SrTiO3
(001) substrates by laser MBE.38 Two superlattices with three
repeats of YBCO/LCMO heterostructures have been experi-
mentally studied. The thicknesses of individual LCMO layers
were �10 nm (26 unit cells) in both samples while the thick-
nesses of YBCO layers in the two samples are �10 nm (9 unit
cells) and �5 nm (5 unit cells), or (YBCO)9/(LCMO)26 and
(YBCO)5/(LCMO)26, respectively. In addition, for the refer-
ence purpose, the single layer films of YBCO and LCMO of
the same thickness of �50 nm have been grown under same
growth condition. We discuss the measurements performed at
room temperature to uncover the effect of periodic structure
on the coherent phonon behavior. Time-resolved pump-probe
measurements were performed with femtosecond pulses from
a kHz Ti:sapphire regenerative amplifier (90 fs, Libra,
Coherent, Inc.) as briefly described in the inset of Fig. 1(a).
a)[email protected])[email protected]
0003-6951/2016/108(13)/132601/5/$30.00 VC 2016 AIP Publishing LLC108, 132601-1
APPLIED PHYSICS LETTERS 108, 132601 (2016)
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 129.15.31.185 On: Thu, 19 May 2016
23:52:30
The fundamental output at 800 nm was used as the pump beam
which excited normally onto the sample. An optical parametric
amplifier system (Opera Sola, Coherent, Inc.) pumped by the
regenerative amplifier is employed as the probe beam for
wavelength-dependent measurements. The incident angle of
the probe beam is �15� so that the scattering angle is �5�
inside the sample with a refractive index of �2.5. In our
experiments, the pump fluence was set at �500 lJ/cm2 while
the probe pulse was about two orders of magnitude weaker.
The absorption lengths at a wavelength of 800 nm are
�100 nm in both YBCO and LCMO, so that the excitation
penetrates through the superlattice samples. The energy
absorbed by the superlattice sample can induce a transient tem-
perature increase of <20 K. The diameter of pump laser spot
was set to be �1 mm, which is orders of magnitude larger than
the sample thickness.
Figure 1(a) shows a typical pump-probe trace recorded
from the (YBCO)9/(LCMO)26 superlattice sample probed at
480 nm. As seen, following an abrupt change in reflectivity,
the recovery dynamics is manifested as a multi-exponential
decay entangled with periodic oscillations. The exponential
decay dynamics is attributed to the dynamics of photo-induced
quasiparticles.39 Here, we mainly concern the oscillatory
components after subtracting off the exponential decay contri-
bution (inset, Fig. 1(b)). As clearly seen, the oscillatory signal
consists of two different modes: a fast oscillation that damps
strongly at the early stage (<20 ps) and a slow oscillation that
persists to a longer time (>300 ps). To quantify the oscillation
frequencies, we performed a Fourier transformation. The
Fourier spectrum shown in Fig. 1(b) indicates the presence of
the two modes at 81 and 236 GHz that are well separated in
the frequency domain.
Next we discuss the possible underlying mechanisms for
the two distinct oscillatory modes. First we note that for the
light-absorbing ultrathin film grown on a bulk substrate, the
absorbing layer may act as a transducer where a pulse of coher-
ent acoustic phonons is generated by the pump beam.40–42
After that, the strain pulse (coherent acoustic phonons) gener-
ated in the film may propagate into the substrate, thus inducing
changes in reflectivity of the probe pulse. This effect has been
frequently discussed in the scheme of stimulated Brillouin scat-
tering where the probe beam reflected by the propagating strain
interferes with the light reflected at the surface, resulting in
oscillations in the pump-probe traces.22,40,42 In this process, the
oscillation frequency f depends on the probe wavelength (k)
as19,22,40–42
f ¼ tq
2p¼ 2n kð Þt
kcos h; (1)
where nðkÞ, t, q and h are the wavelength-dependent refrac-
tive index, the propagation velocity of the strain pulse, the
acoustic wave vector, and the scattering angle, respectively.
To check whether such a picture is indeed responsible for
the oscillation modes observed here, we have performed
experiments with different probe wavelengths (Fig. 2(a)). As
seen, the two oscillatory components show different depend-
ences on the probe wavelength. Specifically, the frequency
of early stage fast oscillation is almost independent of the
probe wavelength, whereas the frequency of the slow mode
decreases significantly with increasing probe wavelength. In
addition, as shown in Fig. 2(b), the frequency of slow mode
is linearly dependent on nðkÞ=k (i.e., the wave vector) and
can be well fitted to Equation (1), suggesting that the slow
component is indeed relevant to the stimulated Brillouin
scattering. To further confirm such assignments, we have
performed additional control measurements on the reference
FIG. 1. (a) Pump-probe trace recorded from the [(YBCO)9/(LCMO)26]� 3
superlattice sample with probe wavelength at 480 nm. The inset shows a dia-
gram of pump-probe spectroscopy. (b) Fourier transformation of the oscilla-
tion component shows two oscillating modes with frequencies at 81 GHz
and 236 GHz, respectively. The inset shows the oscillatory component
obtained by subtracting off the multi-exponential decay component.
FIG. 2. (a) The oscillatory component
probed at different wavelengths. (b)
Frequencies of the two oscillatory modes
are plotted as a function of the wave
vector. The slow oscillation frequency
can be well produced by Equation (1)
(green squares), while the fast oscillation
frequency is nearly independent of the
probe wavelength (blue circles).
132601-2 Li et al. Appl. Phys. Lett. 108, 132601 (2016)
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 129.15.31.185 On: Thu, 19 May 2016
23:52:30
samples of pure YBCO and LCMO films, where the effects
from the YBCO/LCMO interface are absent. After subtract-
ing off the multi-exponential decay components, the experi-
mental data shown in Fig. 3 reveal that the pump-probe
signals from all three samples exhibit slow oscillations with
the same frequency. The results immediately imply that
the primary origin of the slow component is the propagation
of coherent phonons in SrTiO3 substrates that are initially
launched in the transducer of superlattice film (see Fig.
3(b)).41 From the slope in Fig. 2(b), the sound velocity
can be evaluated to be �7950 m/s, which is consistent with
the acoustic velocity in SrTiO3 from literature.40 The mean
free path for the slow mode in SrTiO3 probed at 480 nm is
�1.6 lm.
The fast oscillation mode, however, is more intriguing
since it is independent of the probe wavelength and is only
observed in the superlattice sample (see Fig. 3). To elucidate
this, we also note that in correlated oxide materials with
complex phase diagrams besides coherent acoustic phonons,
the oscillatory signals in pump-probe traces may also be gen-
erated by some collective modes such as coherent optical
phonons or magnetic excitations (i.e., magnons). First, we
point out that the fast oscillation mode is unlikely to be con-
nected with optical phonons since the observed oscillation
frequency (236 GHz) is quite low and the signal is independ-
ent of the polarization of incident beams. At the same time,
the magnetic origin of the signal is also unlikely since the
measurement is performed at room temperature, which is
well above the Neel temperature. Finally, we attempt to
understand this mode by considering the specular reflection
of acoustic phonons at the oxide interface. Toward this, con-
sidering the well-defined sharp interfaces for the superlattice
structure,43 the pump-induced phonon pulse may be reflected
in a coherent manner by the interfaces that modulates the
light reflectivity.1,5 Previously, phononic reflection at the
interface between superlattice and buffer layer has been
observed with echo signals in differential reflectivity in
Bi2Te3/Sb2Te3 superlattice.44 In our samples, the phonon
reflections at the interfaces inside the superlattices may cause
acoustic wave interference. Such an effect can be analyzed
with a model considering the phonon Bragg reflection.45 At
quasi-normal incidence, the Bragg condition requires 2D=kA
to be an integer, where D is the period of superlattice and kA
is the phonon wavelength. Thus, the center frequency (f ) for
the mini Brillouin zone can be expressed as45
f ¼ tef f
D: (2)
Here, tef f is the effective sound velocity in the superlattice
that can be approximately given by45
D
tef f¼ dY
tYþ dL
tL; (3)
where dY , dL, tY , and tL are the layer thicknesses of and
propagation velocities in the YBCO and LCMO layers,
respectively. This model predicts that the oscillation fre-
quency is sensitive to the layer thickness but independent of
the probe wavelength.
To check the plausibility of this scenario as the origin
of the fast oscillation mode, we compare the experimental
data recorded from the two superlattice samples (YBCO)9/
(LCMO)26 and (YBCO)5/(LCMO)26, with the only differ-
ence in the thickness of YBCO layer. Figure 4(a) shows the
obtained pump-probe traces recorded from the two samples.
As clearly seen in Fig. 4(a), the frequency of slow oscillation
mode remains the same while the fast mode shows a very
strong variation with YBCO thickness, indicating that this
fast mode is indeed of the intrinsic response from the peri-
odic structure. More specifically, the frequency of the fast
mode increases from 236 GHz in the (YBCO)9/(LCMO)26
superlattice to 351 GHz in the (YBCO)5/(LCMO)26 superlat-
tice. To highlight the difference, we plot the differential of
the signal in time domain in Fig. 4(b). The experimental data
can be quantitatively compared with the theoretical values
estimated from the model. By using literature values of the
sound velocity in YBCO46 and LCMO47 bulk materials, the
calculated frequencies from Equation (2) yield 257 GHz for
(YBCO)9/(LCMO)26 and 348 GHz for (YBCO)5/(LCMO)26,
respectively. Both values are in remarkable agreements with
the experimentally measured data. Moreover, the time con-
stants for the amplitude damping of the fast components are
FIG. 3. (a) Transient reflectivity signals of YBCO, LCMO, and SL films
probed at 800 nm are shown in a scale normalized to the signal at zero delay.
The slow oscillation components are shown in the insets. (b) Fourier trans-
formation indicates the frequencies of the slow component are the same in
the three samples.
FIG. 4. (a) Pump-probe signals recorded from two superlattices with different
thicknesses of YBCO layer. The signals are recorded with probe wavelength
of 400 nm. (b) The differential signal shows a clear structure dependence of
the fast oscillation component.
132601-3 Li et al. Appl. Phys. Lett. 108, 132601 (2016)
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 129.15.31.185 On: Thu, 19 May 2016
23:52:30
�12 ps and �9 ps, respectively, in the two samples, giving
the mean free paths to be �57 nm and �48 nm, which are
close to the superlattice thicknesses. These facts imply that
the finite superlattice thickness is probably the primary limit
for the phonon propagation, which is also consistent with the
picture of phonon Bragg reflection. The phonons whose
wave vectors satisfy the Bragg condition will be reflected off
the superlattice and be unable to propagate into the substrate,
so that only few oscillations can be observed at the early
stage (Fig. 4(b)).
Although the scenario of phononic Bragg reflection can
well describe the fast modes, it is worth noting that the free
carrier absorption of metallic layers in our superlattice sam-
ples may also affect the coherent phonon dynamics. In litera-
ture, it has been shown that the electronic coupling induced
modulations give rise to the fast oscillations in metal-
dielectric SrRuO3/SiTiO3 superlattice samples as probed by
ultrafast x-ray diffraction.48–50 This effect may function in
YBCO/LCMO superlattice samples since both the metallic
layers absorb the pump light. The different energy absorbed
in the two metallic materials could possibly cause different
degrees of expansions and set the vibrational modes. The fre-
quency of such oscillations is also dependent on the periodic-
ity of the superlattice where Equation (2) is also applicable.
These results indicate that the coherent behaviors of acoustic
phonons can be effectively controlled in oxide superlattices
through superlattice periodicity.
In summary, we have found two oscillating modes
appearing in ultrafast pump-probe traces due to coherent
acoustic phonons in LCMO/YBCO superlattices. These two
modes show markedly different probe-wavelength dependen-
ces, which can be ascribed as due to the stimulated Brillouin
scattering linked to the light reflection by propagating strain
pulse and the phononic Bragg oscillations or free carrier
absorption, respectively. Our work suggests that artificial
oxide superlattice is a promising structure to manipulate the
coherent phonon scattering. This can be of great importance in
engineering thermal2,3 and acoustic properties for potential
applications such as coherent heat conductors,5,6 thermal
bandgap materials,1 and acoustic lasers.7,51 It is worth noting
that the dynamics of coherent phonons, e.g., the attenuation of
the fast mode, can serve as a metric to characterize the quality
of the oxide interfaces (i.e., shaper interface results in less
attenuation). Moreover, the tunable lattice dynamics in oxide
superlattice, as well as the long range transfer of electron-
phonon coupling in oxide superlattices observed in literature,52
may hold the key to uncover the roles played by electron-
phonon interactions for multiple and often coupled order
parameters (i.e., charge-density wave or pseudogap) of the rich
phase diagram in such strongly correlated materials.47,53,54
The work at Nanjing University was supported by the
National Basic Research Program of China (2013CB932903
and 2012CB921801, MOST) and the National Science
Foundation of China (91233103, 11574140, 11227406, and
11321063). J.C. and X.L. acknowledge the support by the
Department of Energy under Grant No. DE-SC0012375.
S.M. was funded by the DOD-ARO under Grant No. 0402-
17291. The authors acknowledge Dr. Xuewei Wu for his
technical assistance.
1M. Maldovan, Nat. Mater. 14, 667 (2015).2S. Alaie, D. F. Goettler, M. Su, Z. C. Leseman, C. M. Reinke, and I. El-
Kady, Nat. Commun. 6, 7228 (2015).3N. Zen, T. A. Puurtinen, T. J. Isotalo, S. Chaudhuri, and I. J. Maasilta,
Nat. Commun. 5, 3435 (2014).4J. Ravichandran, A. K. Yadav, R. Cheaito, P. B. Rossen, A. Soukiassian,
S. J. Suresha, J. C. Duda, B. M. Foley, C. H. Lee, Y. Zhu, A. W.
Lichtenberger, J. E. Moore, D. A. Muller, D. G. Schlom, P. E. Hopkins,
A. Majumdar, R. Ramesh, and M. A. Zurbuchen, Nat. Mater. 13, 168
(2013).5M. Maldovan, Nature 503, 209 (2013).6M. N. Luckyanova, J. Garg, K. Esfarjani, A. Jandl, M. T. Bulsara, A. J.
Schmidt, A. J. Minnich, S. Chen, M. S. Dresselhaus, Z. Ren, E. A.
Fitzgerald, and G. Chen, Science 338, 936 (2012).7R. P. Beardsley, A. V. Akimov, M. Henini, and A. J. Kent, Phys. Rev.
Lett. 104, 085501 (2010).8E. L. Thomas, T. Gorishnyy, and M. Maldovan, Nat. Mater. 5, 773 (2006).9R. M. Costescu, D. G. Cahill, F. H. Fabreguette, Z. A. Sechrist, and S. M.
George, Science 303, 989 (2004).10M. V. Simkin and G. D. Mahan, Phys. Rev. Lett. 84, 927 (2000).11J.-K. Yu, S. Mitrovic, D. Tham, J. Varghese, and J. R. Heath, Nat.
Nanotechnol. 5, 718 (2010).12M. S. Kushwaha, P. Halevi, L. Dobrzynski, and B. Djafarirouhani, Phys.
Rev. Lett. 71, 2022 (1993).13M. Sigalas and E. N. Economou, Sol. State Commun. 86, 141 (1993).14B. Li, Nat. Mater. 9, 962 (2010).15B. Liang, X. S. Guo, J. Tu, D. Zhang, and J. C. Cheng, Nat. Mater. 9, 989
(2010).16T. Gorishnyy, C. K. Ullal, M. Maldovan, G. Fytas, and E. L. Thomas,
Phys. Rev. Lett. 94, 115501 (2005).17B. W. Li, L. Wang, and G. Casati, Phys. Rev. Lett. 93, 184301 (2004).18B. Liang, B. Yuan, and J.-C. Cheng, Phys. Rev. Lett. 103, 104301 (2009).19L. Cheng, C. La-o-Vorakiat, C. S. Tang, S. K. Nair, B. Xia, L. Wang, J.-X.
Zhu, and E. E. M. Chia, Appl. Phys. Lett. 104, 211906 (2014).20C. He, M. Grossmann, D. Brick, M. Schubert, S. V. Novikov, C. T. Foxon,
V. Gusev, A. J. Kent, and T. Dekorsy, Appl. Phys. Lett. 107, 112105
(2015).21A. Bartels, T. Dekorsy, H. Kurz, and K. Kohler, Appl. Phys. Lett. 72, 2844
(1998).22C. Thomsen, H. T. Grahn, H. J. Maris, and J. Tauc, Phys. Rev. B 34, 4129
(1986).23C. Thomsen, J. Strait, Z. Vardeny, H. J. Maris, J. Tauc, and J. J. Hauser,
Phys. Rev. Lett. 53, 989 (1984).24F. Vall�ee and F. Bogani, Phys. Rev. B 43, 12049 (1991).25S. D. Silverstri, G. Cerullo, and G. Lanzani, Coherent Vibrational
Dynamics (CRC Press, 2008).26A. A. Maznev, F. Hofmann, A. Jandl, K. Esfarjani, M. T. Bulsara, E. A.
Fitzgerald, G. Chen, and K. A. Nelson, Appl. Phys. Lett. 102, 041901
(2013).27P.-A. Mante, Y.-C. Wu, Y.-T. Lin, C.-Y. Ho, L.-W. Tu, and C.-K. Sun,
Nano Lett. 13, 1139 (2013).28M. N. Luckyanova, J. A. Johnson, A. A. Maznev, J. Garg, A. Jandl, M. T.
Bulsara, E. A. Fitzgerald, K. A. Nelson, and G. Chen, Nano Lett. 13, 3973
(2013).29A. A. Maznev, K. J. Manke, K.-H. Lin, K. A. Nelson, C.-K. Sun, and J.-I.
Chyi, Ultrasonics 52, 1 (2012).30C. Aku-Leh, K. Reimann, M. Woerner, E. Monroy, and D. Hofstetter,
Phys. Rev. B 85, 155323 (2012).31A. Bruchhausen, A. Fainstein, A. Soukiassian, D. G. Schlom, X. X. Xi, M.
Bernhagen, P. Reiche, and R. Uecker, Phys. Rev. Lett. 101, 197402
(2008).32A. Yamamoto, T. Mishina, Y. Masumoto, and M. Nakayama, Phys. Rev.
Lett. 73, 740 (1994).33A. Bartels, T. Dekorsy, H. Kurz, and K. Kohler, Phys. Rev. Lett. 82, 1044
(1999).34W. S. Capinski, H. J. Maris, T. Ruf, M. Cardona, K. Ploog, and D. S.
Katzer, Phys. Rev. B 59, 8105 (1999).35K. Mizoguchi, M. Hase, and S. Nakashima, Phys. Rev. B 60, 8262 (1999).36C.-K. Sun, J.-C. Liang, C. J. Stanton, A. Abare, L. Coldren, and S. P.
DenBaars, Appl. Phys. Lett. 75, 1249 (1999).37C.-K. Sun, J.-C. Liang, and X.-Y. Yu, Phys. Rev. Lett. 84, 179 (2000).38J. Chakhalian, J. W. Freeland, H. U. Habermeier, G. Cristiani, G.
Khaliullin, M. van Veenendaal, and B. Keimer, Science 318, 1114 (2007).39W. Li, C. Zhang, X. Wang, J. Chakhalian, and M. Xiao, J. Magn. Magn.
Mater. 376, 29 (2015).
132601-4 Li et al. Appl. Phys. Lett. 108, 132601 (2016)
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 129.15.31.185 On: Thu, 19 May 2016
23:52:30
40S. Brivio, D. Polli, A. Crespi, R. Osellame, G. Cerullo, and R. Bertacco,
Appl. Phys. Lett. 98, 211907 (2011).41Y. H. Ren, M. Trigo, R. Merlin, V. Adyam, and Q. Li, Appl. Phys. Lett.
90, 251918 (2007).42E. Pontecorvo, M. Ortolani, D. Polli, M. Ferretti, G. Ruocco, G. Cerullo,
and T. Scopigno, Appl. Phys. Lett. 98, 011901 (2011).43T. Y. Chien, L. F. Kourkoutis, J. Chakhalian, B. Gray, M. Kareev, N. P.
Guisinger, D. A. Muller, and J. W. Freeland, Nat. Commun. 4, 2336
(2013).44Y. Wang, C. Liebig, X. Xu, and R. Venkatasubramanian, Appl. Phys. Lett.
97, 083103 (2010).45Y. Ezzahri, S. Grauby, J. M. Rampnoux, H. Michel, G. Pernot, W. Claeys,
S. Dilhaire, C. Rossignol, G. Zeng, and A. Shakouri, Phys. Rev. B 75,
195309 (2007).46D. P. Almond, G. A. Saunders, and E. F. Lambson, Superconduct. Sci.
Tech. 1, 163 (1988).47Y. Ren, G. L€upke, Y. Hu, Q. Li, C. S. Hong, N. H. Hur, and R. Merlin,
Phys. Rev. B 74, 012405 (2006).
48M. Herzog, W. Leitenberger, R. Shayduk, R. M. van der Veen, C. J.
Milne, S. L. Johnson, I. Vrejoiu, M. Alexe, D. Hesse, and M. Bargheer,
Appl. Phys. Lett. 96, 161906 (2010).49A. Bojahr, D. Schick, L. Maerten, M. Herzog, I. Vrejoiu, C. v. K.
Schmising, C. Milne, S. L. Johnson, and M. Bargheer, Phys. Rev. B 85,
224302 (2012).50M. Herzog, R. Shayduk, W. Leitenberger, R. M. van der Veen, C. J.
Milne, S. L. Johnson, I. Vrejoiu, M. Alexe, D. Hesse, and M. Bargheer, in
International Conference on Ultrafast Phenomena (2010).51W. Maryam, A. V. Akimov, R. P. Campion, and A. J. Kent, Nat.
Commun. 4, 2184 (2013).52N. Driza, S. Blanco-Canosa, M. Bakr, S. Soltan, M. Khalid, L. Mustafa, K.
Kawashima, G. Christiani, H. U. Habermeier, G. Khaliullin, C. Ulrich, M.
Le Tacon, and B. Keimer, Nat. Mater. 11, 675 (2012).53O. V. Misochko, N. Georgiev, T. Dekorsy, and M. Helm, Phys. Rev. Lett.
89, 067002 (2002).54J. P. Hinton, J. D. Koralek, Y. M. Lu, A. Vishwanath, J. Orenstein, D. A.
Bonn, W. N. Hardy, and R. Liang, Phys. Rev. B 88, 060508 (2013).
132601-5 Li et al. Appl. Phys. Lett. 108, 132601 (2016)
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 129.15.31.185 On: Thu, 19 May 2016
23:52:30