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Spectroscopic evidence for negative electronic compressibility in a quasi-three-dimensional spin–orbit correlated metal


Negative compressibility is a sign of thermodynamic instability of open1,2,3 or non-equilibrium4,5 systems. In quantum materials consisting of multiple mutually coupled subsystems, the compressibility of one subsystem can be negative if it is countered by positive compressibility of the others. Manifestations of this effect have so far been limited to low-dimensional dilute electron systems6,7,8,9,10,11. Here, we present evidence from angle-resolved photoemission spectroscopy (ARPES) for negative electronic compressibility (NEC) in the quasi-three-dimensional (3D) spin–orbit correlated metal (Sr1−xLax)3Ir2O7. Increased electron filling accompanies an anomalous decrease of the chemical potential, as indicated by the overall movement of the deep valence bands. Such anomaly, suggestive of NEC, is shown to be primarily driven by the lowering in energy of the conduction band as the correlated bandgap reduces. Our finding points to a distinct pathway towards an uncharted territory of NEC featuring bulk correlated metals with unique potential for applications in low-power nanoelectronics and novel metamaterials.

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Figure 1: Fermi surface and band structure of (Sr1−xLax)3Ir2O7 forx = 0.057.
Figure 2: Chemical potential shift on electron doping in (Sr1−xLax)3Ir2O7.
Figure 3: Doping evolution of the valence band top and conduction band bottom of (Sr1−xLax)3Ir2O7.
Figure 4: Doping evolution of the band structure of (Sr1−xLax)3Ir2O7 and its comparison with Nd2−xCexCuO4.

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We thank K. S. Burch, T-R. Chang, Y-H. Chu, A. Fujimori, Z. Hussain, S. A. Kivelson, H. Lin, V. Madhavan, Z-X. Shen, Q. Si, C. M. Varma, Z-Y. Weng, H. Yao and X. J. Zhou for discussions, and K. Tanaka for measuring sample work functions at UVSOR, Japan. The work at Boston College was supported by a BC start-up fund (J.H., R-H.H.), the US NSF CAREER Awards DMR-1454926 (R-H.H., in part) and DMR-1056625 (T.H., C.D., X.C., S.D.W.), NSF Graduate Research Fellowship GRFP-5100141 (T.R.M.), DOE DE-SC0002554 and DE-FG02-99ER45747 (Z.W.) and the W. M. Keck Foundation (M.J.N.). The work at Northeastern University (NU) was supported by the DOE, BES Contract No. DE-FG02-07ER46352, and benefited from NU’s ASCC and the allocation of supercomputer time at NERSC through DOE grant DE-AC02-05CH11231. Photoemission experiments were performed at the SSRL and ALS, supported respectively by the US DOE BES Contract Nos. DE-AC02-76SF00515 and DE-AC02-05CH11231, at HSRC and SPring-8 (preliminary) with the approval of Proposal Nos 14-A-1 and 2014B1501.

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Authors and Affiliations



J.H. and T.H. contributed equally to this work. J.H. and R-H.H. proposed and designed the research. J.H. and T.R.M. carried out the ARPES measurements with help from Y.H., J.D.D., S-K.M., Q.L. and H.P. T.H., C.D. and X.C. grew the samples. T.H., J.H. and T.R.M. characterized the samples with EDS. H.H. and R.S.M. performed the first-principles calculations and, along with A.B. and K.K., provided theoretical guidance. M.H., D.H.L., S-K.M., M.A. and K.S. maintained the experimental facilities. J.H. analysed the data with help from Y.Z. J.H. and R-H.H. wrote the paper with key inputs from Z.W., Y.H., S.D.W., A.B. and R.S.M. R-H.H., S.D.W., M.J.N. and A.B. are responsible for project direction, planning and infrastructure.

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Correspondence to Rui-Hua He.

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He, J., Hogan, T., Mion, T. et al. Spectroscopic evidence for negative electronic compressibility in a quasi-three-dimensional spin–orbit correlated metal. Nature Mater 14, 577–582 (2015).

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