The retention at ambient of the high-pressure-induced metastable superconducting phases in antimony single crystals
Graphical abstract
Introduction
High pressure has been shown to be effective for achieving high-temperature superconductivity. This has been amply exemplified, for example, by the current record high Tcs of 164 K in the cuprate HgBa2Ca2Cu3O8+δ under ~31 GPa [1] and 260 K in the hydrogen-rich molecular solid LaH10 under ~ 200 GPa [2,3]. These impressive record high Tcs are scientifically significant. Their technological impacts would be profound and limited only by imagination should these superconducting states under high pressures be retained at ambient. To examine such a possibility, we have chosen Sb as a model system because of the existence of several high-pressure-induced metastable superconducting phases achieved through first-order phase transitions [4]. A first-order transition usually exhibits a hysteresis in pressure and/or temperature cycling due to the associated latent heat. Such latent heat may serve as an energy barrier to protect the metastable phase against the removal of pressure when following a specific thermodynamic path. Indeed, we have successfully retained two high-pressure-induced metastable superconducting phases, the m-HGL phase with a Tc of 3.4 K and the bcc phase with a Tc of 4.0 K, at up to 135 K and 110 K, respectively, after the rapid removal of pressure (pressure-quench) at 77 K.
Antimony is an interesting group 15 semi-metallic element with unusual phonon and electron energy spectra. It undergoes a series of structural phase transitions under different pressures [4]. For instance, with increasing pressure, it has been shown to transform from a rhombohedral (A7) structure (Phase I) at ambient to an incommensurate composite phase with a monoclinic host-guest lattice (m-HGL) (Phase II) at ~ 7 GPa, an incommensurate composite phase with a tetragonal host-guest lattice (t-HGL) (Phase III) at ~ 9 GPa, a bcc lattice (Phase IV) mixed with t-HGL starting at ~ 22 GPa, and finally a single bcc phase at 28 GPa, as displayed in Fig. 1. Antimony exhibits high mobility carriers and displays nontrivial topological surface states. The high mobility carriers together with an almost perfect compensation band structure allow Sb to show the largest unsaturated magnetoresistance among all elements at ambient, characteristic of a topological solid [5]. This is consistent with the topological surface state observed by scanning tunneling microscopy [6] and angle-resolved photoemission spectroscopy [7], suggesting its possible nanoscale device applications.
Section snippets
Methods
For our investigation, pressure was applied to the samples by using a Mao-Bell type diamond anvil cell with a culet size of 300 μm. The stainless steel gasket is insulated with Stycast 2850. The sample chamber diameter is 120 μm and sodium chloride or boron nitride serves as the pressure medium. The measured samples were cut into thin squares with diagonal of ~100 μm and thickness of ~10 μm from an antimony ingot (Cominco American Inc., 99.9999% purity). The sample pressure was determined by
Results and discussion
Single-crystalline Sb samples with an orientation of rhombohedral (111) direction were used in this study. The large dc resistance ratio, R(300 K)/R(2 K) ~ 500, and the huge magnetoresistance, [R(9 T) – R(0 T)]/R(0 T) ~ 10E5 at 2 K, are indicative of the high quality of our samples. The room-temperature R was determined as a function of pressure up to 63 GPa and is shown in Fig. 1. Under increasing pressure, R decreases rapidly and smoothly by ~60% up to ~6 GPa in the Phase I region; jumps
Conclusion
We have investigated the phase diagram of Sb up to 63 GPa and down to 1.2 K, resistively, and identified the sequence of phase transitions from I (rhombohedral lattice) → II (monoclinic host-guest lattice) → III (tetragonal host-guest lattice) → IV (bcc lattice) at room temperature. The I → II and III → IV transitions are thermodynamically first-order in nature with a large hysteresis in temperature and/or pressure cycling. By taking advantage of such a hysteresis, we have successfully retained
Data availability
The data that support the plots and findings within this paper are available from the corresponding authors upon reasonable request.
Credit author statement
C.W.C. conceived and supervised the project. Z.W., L.D., and M.G. designed the experiments. Z.W. and S. H. carried out the experiments. Z.W. analyzed the results and drafted the paper. Z. W. and C.W.C. finalized the paper. All authors discussed the results and edited and commented on the manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The work is supported by US Air Force Office of Scientific Research Grants FA9550-15-1-0236 and FA9550-20-1-0068, the T. L. L. Temple Foundation, the John J. and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston.
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