Science Journals — AAASSCIENCE sciencemag.org RETRACTION POST DATE • 24 APRIL 2020 1 After the...

RETRACTION POST DATE • 24 APRIL 2020 1SCIENCE sciencemag.org

After the publication of our Research Article “Current-induced strong diamagnetism in the Mott insulator Ca

2RuO

4” (1), new measurements performed in Kyoto by Giordano Mattoni et al. (2) revealed a serious

technical artifact that affected our published data. Specifically, it became clear that a large part of the reported diamagnetic signal arose from a mechanism that we did not anticipate. This signal is attributable to localized heating of the sample holder, caused by the unavoidable Joule heating in the sample.

The published data in Figs. 1A, 1C, and 2B are affected by this artifact. The theoretical model of Fig. 3 remains valid, as it deals with the generic case in which a Mott gap is suppressed. Because the artifact affects the main experimental data, the authors unanimously agreed to retract the Research Article. For the same reason, another work on Ca

3(Ru

1−xTi

x)

2O

7 by some of the present authors published in Physical Review Letters (3) is

also being retracted (4).

Chanchal Sow1, Shingo Yonezawa1, Sota Kitamura2,3, Takashi Oka3,4, Kazuhiko Kuroki5, Fumihiko Nakamura6, Yoshiteru Maeno1*

1Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan. 2Department of Physics, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan. 3Max Planck Institute for the Physics of Complex Systems, D-01187 Dresden, Germany. 4Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany. 5Department of Physics, Graduate School of Science, Osaka University, Osaka 560-0043, Japan. 6Department of Education and Creation Engineering, Kurume Institute of Technology, Fukuoka 830-0052, Japan.

*Corresponding author. Email: [email protected]

Retraction

10.1126/science.abc0469

Post date 24 April 2020

REFERENCES AND NOTES

1. C. Sow et al, Science 358 1084 (2017).2. G. Mattoni, S. Yonezawa, Y. Maeno, arXiv:2004.04570 (2020).3. C. Sow et al, Phys. Rev. Lett. 122, 196602 (2019).4. C. Sow et al, Phys. Rev. Lett. 124, 169902 (2020).

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SOLID-STATE PHYSICS

Current-induced strong diamagnetismin the Mott insulator Ca2RuO4Chanchal Sow,1* Shingo Yonezawa,1 Sota Kitamura,2,3 Takashi Oka,3,4

Kazuhiko Kuroki,5 Fumihiko Nakamura,6 Yoshiteru Maeno1*

Mott insulators can host a surprisingly diverse set of quantum phenomena when their frozenelectrons are perturbed by various stimuli. Superconductivity, metal-insulator transition,and colossal magnetoresistance induced by element substitution, pressure, and magnetic fieldare prominent examples. Here we report strong diamagnetism in the Mott insulator calciumruthenate (Ca2RuO4) induced by dc electric current.The application of a current density ofmerely 1 ampere per centimeter squared induces diamagnetism stronger than that in othernonsuperconducting materials.This change is coincident with changes in the transportproperties as the system becomes semimetallic.These findings suggest that dc current may bea means to control the properties of materials in the vicinity of a Mott insulating transition.

In response to an external magnetic field,conduction electrons in a material exhibitcyclotronmotion, resulting in an orbital mag-netic moment. Such orbital motion leads toquantized (discrete) energy levels, known as

the Landau levels. In a simple system, the re-sultant increase in the total energy is propor-tional to the square of the appliedmagnetic field.This increase in energy results in a negative mag-netic susceptibility, which does not depend onthe field strength. This effect is known as theLandau diamagnetism, or orbital diamagnetism(1). Another source of diamagnetism, ubiquitouslypresent irrespective of the metallicity of a mate-rial, is the circulation of inner-shell electrons. Inmost materials, both types of diamagnetism arerather weak and are often hindered by paramag-netic contributions. However, pyrolytic graphiteand bismuth are well known to exhibit excep-tionally large diamagnetism (Fig. 1A), owing tostrong Landau diamagnetism originating fromlight-mass electrons with gapped Dirac disper-sions aswell asmulti-orbital effects (2–4). Recently,relatively large diamagnetism was observed insome topological semimetals such as TaAs, as-cribable to the Weyl electrons in the bulk elec-tronic state (5), againwithDirac-cone dispersion.Here we show that the Mott insulator Ca2RuO4

under dc electric current exhibits diamagnetismstronger than other known nonsuperconductingmaterials (Fig. 1A). Notably, the diamagnetism ofCa2RuO4 at 7 T is comparable to that of high-temperature superconductor YBa2Cu3O7−d. Neg-ativemagnetization stemming from localmagnetic

moments is found in certain ferrimagnets, such asYVO3, which contain two or more magnetic sub-lattices (6). However, such negative magnetizationis associated with the flipping of spontaneouslyordered moments; the differential magnetic sus-ceptibility dM/dH is always positive (7), whereMis magnetization andH is appliedmagnetic field.By contrast, diamagnetism is defined as negativeM induced gradually by an external magneticfield, characterized by negative dM/dH.The Mott insulator Ca2RuO4 (8) is an end

member of the system Ca2−xSrxRuO4, which ex-hibits a rich variety of magnetic, transport, andstructural properties (9–13), including the spin-triplet superconductivity in Sr2RuO4, the otherend member (14). Ca2RuO4 exhibits a metal-to-insulator transition at TMI = 357 K accompaniedby a first-order structural transition character-ized by the flattening of the RuO6 octahedrabelow TMI (15–17). Below TMI, the fourth electronof the Ru4+(4d4) ion predominantly occupiesthe dxy orbital (18). On further cooling, Ca2RuO4undergoes an antiferromagnetic ordering at theNeel temperature TN = 113 K, with the Ru spinsaligning along the orthorhombic b axis [Fig. 1B,(17)]. Resonant x-ray diffraction reveals anotherorder, known as orbital ordering (OO), at TOO~ 260 K (19). Ca2RuO4 can be made metallic bypressure (12), chemical substitution (9), or anelectric field (20), accompanied by a first-orderstructural transition to stretch the RuO6 octahe-dra along the cdirection.However, diamagnetismin the normal state has never been reported inCa2−xSrxRuO4.Here we investigated the transport and mag-

netic properties of Ca2RuO4 single crystals underdc current, as summarized in Fig. 1C. Figure 2Ashows the temperature dependence of the re-sistivity r(T) under various applied currents fora sample with a cross section of about 2.9 ×10−3 cm2. Typical insulating behavior in r(T) isobserved at 10 nA. It is technically difficult topassmoderate current (e.g., 10 nA to 3mA) downto low temperatures owing to the high resistivityof the material (Fig. 1C and fig. S6). However,

with increasing current, it becomes possible toflow current down to 20 K because the resistivitydrops by more than five orders of magnitudewith a current as small as 4mA. The shape of ther(T ) curve changes from that expected for ther-mal activation to a curve shape characteristicof semimetallic behavior with increasing current,consistent with the observed partial closing of theMott gap (21).The magnetization also exhibits substantial

change. As shown in Fig. 2B, the behavior ofM(T) under a current of 10 nA is identical to itsbehavior at zero current (8). However, with in-creasing current,M decreases gradually, and theantiferromagnetic transition is suppressed before2 mA is reached. We speculate that by reducingthemany-body correlation effect, carriers injectedby current promote the itinerant nature of 4delectrons so effectively that the local momentsreadily vanish, melting the antiferromagneticorder. With higher current (4.0 to 5.5 mA),M(T)exhibits a decrease below ~150 K and eventu-ally becomes negative below 50 K. We carefullychecked that this negative signal is not an ex-perimental artifact (fig. S3 to S5). The directionof the magnetization is always antiparallel to theapplied field, regardless of the field and/or cur-rent directions (fig. S4); thus, the local magneticfield induced by external current does not playa role. This invariance also excludes magneto-electric effects observed in multiferroic systems(22) as a possible origin.We emphasize that jouleheating, which certainly raises the actual sampletemperature, cannot explain the diamagnetism(fig. S5), because Ca2RuO4 under ambient con-ditions exhibits positive magnetic susceptibilityat all temperatures (fig. S12). Therefore, we con-clude that the observed negative magnetizationin Ca2RuO4 originates from diamagnetism ofconduction carriers. Interestingly, the observeddiamagnetism exhibits a peculiar anisotropy withrespect to the applied magnetic field directions(fig. S10).Next, we focus on magnetotransport proper-

ties. The longitudinal magnetoresistance (MR)at 7 T under a current of 5 mA exhibits sign re-versal at around 70K (Fig. 2C). Such negativeMRwithout apparent ferromagnetic spin fluctuationsis unusual. The Hall coefficient (RH) under cur-rents of 5 to 9 mA (Fig. 2D) also exhibits signchange below 70 to 80 K, indicating the presenceof multiple types of carriers in the current-induced state with semimetallic behavior.We summarize the present findings in Fig. 1C,

where various characteristic temperatures areplotted as functions of the current density J.Above 0.4 A/cm2, the Mott insulating state grad-ually evolves into a state with semimetallic be-havior, with suppression of the antiferromagneticordering. Above 1.3 A/cm2, strong diamagnetismemerges at temperatures below TDM = 50 K(DM, diamagnetism). TDM stays nearly constantwith increasing current up to 2 A/cm2. We em-phasize that the current used in this study islower than the current required to induce theinsulator tometal transition at room temperature(5 A/cm2) (20).

RESEARCH

Sow et al., Science 358, 1084–1087 (2017) 24 November 2017 1 of 4

1Department of Physics, Graduate School of Science, KyotoUniversity, Kyoto 606-8502, Japan. 2Department of Physics,Graduate School of Science, University of Tokyo, Tokyo113-0033, Japan. 3Max Planck Institute for the Physics ofComplex Systems, D-01187 Dresden, Germany. 4Max PlanckInstitute for Chemical Physics of Solids, D-01187 Dresden,Germany. 5Department of Physics, Graduate School ofScience, Osaka University, Osaka 560-0043, Japan.6Department of Education and Creation Engineering, KurumeInstitute of Technology, Fukuoka 830-0052, Japan.*Corresponding author. Email: [email protected](C.S.); [email protected] (Y.M.)

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To understand the observed transport proper-ties, as well as the strong diamagnetism, we in-troduce a phenomenological model of a semimetaloriginating from the Mott-Hubbard bands. Inthis state, electron and hole pockets with lightquasiparticle masses emerge from the upper andlower Hubbard bands, respectively. The pocketsappear in the parts of momentum space wherethe band hybridization ismost prominent (Fig. 3,A to J). Although this model is somewhat spec-ulative, it is consistent with the experimentalfindings, as explained below. For the modeling,we use a tight-binding approach and start withthe band structure of a hypothetical two-bandmetallic state for Ca2RuO4 [Fig. 3, A and F, and(23), section 5] without electron correlations. Weassume the ferro-orbital ordered states (18): Twoelectrons per Ru4+ ion fully occupy the quasi–two dimensional (2D) orbitals and the other twopartially occupy the quasi-1D orbitals. Thus, theelectronic states close to the Fermi level consistof two half-filled bands originating from the dxzand dyz orbitals with dispersions in the kx and kydirections (fig. S14). The two bands hybridize toform two rounded square–shaped Fermi surfacescalled a (hole band) and b (electron band) (Fig.3A). Note that the orbital mixing caused by octa-hedral distortion is neglected.To account for the electronic correlation and

the Mott insulating nature, we next use a pheno-menological approach proposed in (24, 25). Whenthe effect of electron correlation representedby the self-energy S = D2/[w + D1D(k)] is turnedon [where D1D(k) is uncorrelated 1D dispersionand D is the gap parameter.], a Mott gap imme-diately opens up in the Brillouin zone (BZ) wherethe 1D nature is strongly preserved on the G-MandM-X lines (Fig. 3B). The hybridization forcesthe two 1D bands to repel each other, pushing


Ω

Fig. 2. Diamagnetic semimetal behavior in Ca2RuO4. (A) Temperature dependence of the resistivityunder various applied currents. The inset shows a photo of a Ca2RuO4 crystal (sample #1, dimensionsabout 3 mm by 0.9 mm by 0.3 mm) with the two-probe setting. W, ohm. (B) Temperature dependence ofthe magnetization under various applied currents. The strong diamagnetism is observed for currentslarger than 4 mA. Such behavior is consistently reproducible in all of the samples (fig. S7). (C) Thetemperature dependence of the magnetoresistance ratio [r(H) − r(0)]/r(0) at 7 T. The inset showsr(H)/r(0) as a function of applied magnetic field at 20 and 300 K. (D) Hall coefficient (RH) as a functionof temperature for three samples. RH is derived from the linear fitting of the Rxy-H data with magneticfield up to 7 T. The upper inset shows the Hall resistance as a function of magnetic field measuredat various temperatures. The lower inset shows a photo of sample #5 (about 2.7 mm by 0.7 mmby 0.5 mm) with the six-probe setting. I, current leads; V, voltage leads.

Fig. 1. Strongdiamagnetism isobserved in Ca2RuO4.(A) Diamagnetism inCa2RuO4 (undercurrent) comparedwith that in otherdiamagnets andsuperconductors,demonstratingthat Ca2RuO4 undercurrent exhibitsa diamagnetismstronger than thatof other non-superconductingmaterials at similartemperatures. Here,−M is plotted as afunction of applied

10-3 10-2 10-1 100 10110-2

10-1

100

101

102

HOPG

TaAs

Bi

Ca2RuO4Pb

Nb

–M (

mc/ume

3 )

µ0H (T)

YBa2Cu3O7–δ

ao

co

bo

0.0 0.5 1.0 1.5 2.00

100

200

300

400

TN

TDM

TPM-Semimetal (PM-SM)

Diamagnetic-SMAntiferromagnetic-Insulator(AF-I)

PM-Ins.(PM-I)

T (

K)

J (A/cm2)

Paramagnetic-Metal (PM-M)

TMI

Unexplored region

p

magnetic field [m0H] for: Ca2RuO4 at 1.5 A/cm2 and 20 K, highly ordered

pyrolytic graphite (HOPG) at 20 K, bismuth (Bi) at 14 K (30), TaAs at5 K (5), Pb (type I superconductor) at 4.7 K (31), Nb (type II superconductor)at 4.7 K (31), and YBa2Cu3O7−d (type II superconductor) at 4.2 K (31).We obtained the data for Ca2RuO4 and HOPG ourselves. emu,electromagnetic units. (B) Crystal structure of Ca2RuO4. The primitive

vectors ao, bo, and co are defined in the orthorhombic notation. Themagnetic structure in the antiferromagnetic state under zero current isillustrated by arrows. (C) Various characteristic temperatures of Ca2RuO4versus current density. The Mott insulating state evolves into a state withsemimetallic behavior under current, exhibiting diamagnetism above1.3 A/cm2 and below TDM = 50 K.

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one downward and the other upward, as shownin the magnified band dispersion in Fig. 3K. Inthe middle of the G-X line, where the hybrid-ization is strongest, the Hubbard bands form astructure reminiscent of electron-hole pocketsin an indirect-gap semiconductor or semimetal.The bottom of the upper Hubbard band (UHB)with a character is given by ±D − 2g and the topof the lower Hubbard band (LHB) with b char-acter by ±D + 2g, where g is the hybridizationparameter [see (23), section 5(b)]. For a smallcorrelation (D < 2g), the bottom of the a-UHBand the top of the b-LHB form a Fermi arc–likestructure (Fig. 3, B and C). These Fermi arcsshrink as the electron correlation is increased,resulting in a pair of small electron-hole pocketson the G-X line (Fig. 3D) at D ∼ 2g (Fig. 3K). Ascorrelations are increased further, the gap fullyopens, and the formation of the UHB and LHB iscompleted (Fig. 3J). In our experimental system,the tuning of the electronic correlations is achieved

by varying the current (21); the possible mecha-nisms for this tuning are discussed below.When the system approaches the insulator-to-

semimetal transition (i.e., for D = 24 meV), theeffective bandmassm* becomes light for both theUHB and LHB (Fig. 3K). According to the Landaupicture, diamagnetism is inversely proportionalto m*. Thus, we expect large diamagnetism. Theassociated momentum-resolved contribution ofthe orbital susceptibility L(k) [see (23), section5(b)] indeed exhibits sharp peaks at the band edges(Fig. 3L). The total orbital magnetic susceptibil-ity is obtained by integrating L(k) over the BZ(Fig. 3M). In the vicinity of the full gap opening(D = 24meV), a large diamagnetismwith a sharpdrop in susceptibility below a certain temper-ature is derived. With this value of D, the signchange of the calculated magnetic susceptibil-ity occurs at 32 K, agreeing reasonably with theexperimental observation of the negative sus-ceptibility below TDM = 50 K. In spite of such

qualitative agreements in the temperature de-pendence, the size of the calculated diamagnetismis an order of magnitude smaller than that ob-served. Section 5(c) of (23) gives an intuitive ex-planation of the negative susceptibility and itstemperature dependence: The UHB and LHB ofthe Mott insulator act as the conduction andvalence bands. With the gap closing, they formtiny electron and hole pockets; the strong dia-magnetism originates from the orbital motions ofthermally excited quasiparticles on these pockets.One of the remaining issues to be resolved is

the mechanism by which the Mott gap is closedby a dc electric current; although experimentally,such an occurrence has been established (21). Onepossiblemechanism is the increase in the effectiveelectron temperature in the nonequilibrium stateunder dc current. This mechanism has been con-sidered to explain the suppression of ferromagneticordering (26) and melting of charge density waves(27) in strongly correlated electron systems. As


Fig. 3. Electronic structure and diamagnetism of Ca2RuO4 inducedby electric current. (A to E) 2D projection of the Fermi surface at variousbare Mott gaps 2D, starting from the tight-binding model for Ca2RuO4.p, the size of the first Brillouin zone in the unit of 1/at; at, the latticeprimitive vector in the tetragonal notation; ao*, reciprocal primitive vectorin the orthorhombic notation; at*, reciprocal primitive vector in thetetragonal notation. (F to J) Correlated band structures (zero points of theGreen function) corresponding to the cases (A) to (E). Red and blue linesin (A) to (K) indicate the a and b bands, and the brightness of the colorcorresponds to the spectral weight at each point. (A) and (F) represent atwo-band metal without correlations; (B) to (D) and (G) to (I) correspond

to a semimetal; and (E) and (J) represent a Mott insulator. Increasingcurrent corresponds to the change from (E) to (D). (K) Magnified plot of(I) near the Fermi energy. The upper and lower Hubbard bands (UHBand LHB) serve as the electron and hole pockets of the semimetal.(L) Momentum-resolved diamagnetic susceptibility L(k) (at T = 12 K) for D =24 meV. (M) Integrated (sum over k) orbital magnetic susceptibility as afunction of temperature. Large diamagnetic susceptibility emerges in thevicinity of the insulator-semimetal transition (D = 24 meV).The resultsqualitatively agreewith the observed emergence of diamagnetism, including itstemperature dependence. However, the calculated diamagnetism is an order ofmagnitude smaller than that observed.



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an additional mechanism, we speculate that theenhanced screening by the mobile quasiparti-cles reduces the effect of electron correlations.In Ca2RuO4, weakening of the lattice deforma-tion, known to occur by Sr substitution (28) andpressure (29), may take place under current andfurther assist the reduction of the effective cor-relation through the enhancement of the hop-ping energy. To elucidate the relative relevanceof these scenarios, it would be useful to furtherprobe the properties of this material under dccurrent, such as by using photoemission to probethe thermal distribution of electrons and Ramanspectroscopy to probe the softening of phonons.Local electronic properties can be investigatedwith various scanning probes.This work demonstrates that the Mott in-

sulator can be driven to a distinct electronic stateunder nonequilibrium steady-state conditions in-duced by a simple dc electric current. Our workdemonstrates that dc current is a powerful tuningparameter that can be used to explore phases em-erging around the Mott insulating state.

REFERENCES AND NOTES

1. L. Landau, Z. Phys. 64, 629–637 (1930).2. Z. Zhu, A. Collaudin, B. Fauque, W. Kang, K. Behnia, Nat. Phys.

8, 89–94 (2012).

3. H. Fukuyama, Prog. Theor. Phys. 45, 704–729 (1971).4. Y. Fuseya, M. Ogata, H. Fukuyama, J. Phys. Soc. Jpn. 84,

012001 (2015).5. Y. Liu et al., J. Magn. Magn. Mater. 408, 73–76 (2016).6. Y. Ren et al., Nature 396, 441–444 (1998).7. Y. Ren et al., Phys. Rev. B 62, 6577–6586 (2000).8. S. Nakatsuji, S. Ikeda, Y. Maeno, J. Phys. Soc. Jpn. 66,

1868–1871 (1997).9. S. Nakatsuji, Y. Maeno, Phys. Rev. Lett. 84, 2666–2669

(2000).10. O. Friedt et al., Phys. Rev. B 63, 174432 (2001).11. T. Mizokawa et al., Phys. Rev. B 69, 132410 (2004).12. F. Nakamura et al., Phys. Rev. B 65, 220402 (2002).13. S. Nakatsuji et al., Phys. Rev. Lett. 93, 146401 (2004).14. Y. Maeno, S. Kittaka, T. Nomura, S. Yonezawa, K. Ishida,

J. Phys. Soc. Jpn. 81, 011009 (2012).15. C. S. Alexander et al., Phys. Rev. B 60, R8422–R8425 (1999).16. E. Gorelov et al., Phys. Rev. Lett. 104, 226401 (2010).17. M. Braden, G. Andre, S. Nakatsuji, Y. Maeno, Phys. Rev. B 58,

847–861 (1998).18. M. Kubota et al., Phys. Rev. Lett. 95, 026401 (2005).19. I. Zegkinoglou et al., Phys. Rev. Lett. 95, 136401 (2005).20. F. Nakamura et al., Sci. Rep. 3, 2536 (2013).21. R. Okazaki et al., J. Phys. Soc. Jpn. 82, 103702 (2013).22. W. Eerenstein, N. D. Mathur, J. F. Scott, Nature 442, 759–765

(2006).23. See supplementary materials.24. R. M. Konik, T. M. Rice, A. M. Tsvelik, Phys. Rev. Lett. 96,

086407 (2006).25. K.-Y. Yang, T. Rice, F.-C. Zhang, Phys. Rev. B 73, 174501 (2006).26. A. Mitra, A. J. Millis, Phys. Rev. B 77, 220404 (2008).27. S. Ajisaka, H. Nishimura, S. Tasaki, I. Terasaki, Prog. Theor.

Phys. 121, 1289–1319 (2009).28. S. Nakatsuji, Y. Maeno, Phys. Rev. B 62, 6458–6466 (2000).

29. P. Steffens et al., Phys. Rev. B 72, 094104 (2005).30. D. Shoenberg, M. Z. Uddin, Proc. R. Soc. London Ser. A 156,

701–720 (1936).31. A. V. Narlikar, Studies of High Temperature Superconductors:

Advances in Research and Applications (Nova SciencePublishers, 1995), vol. 14.

ACKNOWLEDGMENTS

We acknowledge discussions with J. G. Bednorz. We alsoacknowledge technical support from M. P. Jimenez-Segura. Thiswork was supported by Japan Society for the Promotion of Science(JSPS) Grants-in-Aid for Scientific Research (KAKENHI) (nos.JP26247060, JP15H05852, JP15K21717, and JP17H06136), theJSPS Core-to-Core program, and the Impulsing ParadigmChange through Disruptive Technologies Program (ImPACT)from Japan Science and Technology Agency (JST) (grant no.2015-PM12-05-01). C.S. acknowledges the support of the JSPSInternational Research Fellowship (grant no. JP17F17027). S.K.acknowledges the support of the Advanced Leading GraduateCourse for Photon Science (ALPS). All the relevant data areavailable upon request from the authors.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/358/6366/1084/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S16References (32–41)

25 June 2016; resubmitted 23 January 2017Accepted 5 October 201710.1126/science.aah4297




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http://www.sciencemag.org/content/358/6366/1084/suppl/DC1http://science.sciencemag.org/

4RuO2Current-induced strong diamagnetism in the Mott insulator CaChanchal Sow, Shingo Yonezawa, Sota Kitamura, Takashi Oka, Kazuhiko Kuroki, Fumihiko Nakamura and Yoshiteru Maeno

DOI: 10.1126/science.aah4297 (6366), 1084-1087.358Science

, this issue p. 1084Sciencesimilar materials.nonsuperconducting material. The use of electrical current as a powerful experimental knob may be applicable to other

rose to levels higher than in any other−−the ability to counter an externally applied magnetic field−−diamagnetic response into a semimetal. Concurrently, its 4RuO2 used electrical currents of modest density to turn the Mott insulator Caet al.

Properties of materials can be tuned by various means, such as chemical doping, magnetic field, or pressure. SowTuning diamagnetism with current

ARTICLE TOOLS http://science.sciencemag.org/content/358/6366/1084

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