Charge density wave in layeredLa1−xCexSb2

Abstract

The layered rare-earth diantimonides RSb 2 are anisotropic metals with generally low electronic densities whose properties can be modified by substituting the rare earth. LaSb 2 is a nonmagnetic metal with a low residual resistivity presenting a low-temperature magnetoresistance that does not saturate with the magnetic field. It has been proposed that the latter can be associated to a charge density wave (CDW), but no CDW has yet been found. Here we find a kink in the resistivity above room temperature in LaSb 2 (at 355 K) and show that the kink becomes much more pronounced with substitution of La by Ce along the La 1−x Ce x Sb 2 series. We find signatures of a CDW in x-ray scattering, specific heat, and scanning tunneling microscopy (STM) experiments in particular for x ≈ 0.5. We observe a distortion of rare-earth-Sb bonds lying in-plane of the tetragonal crystal using x-ray scattering, an anomaly in the specific heat at the same temperature as the kink in resistivity and charge modulations in STM. We conclude that LaSb 2 has a CDW which is stabilized in the La 1−x Ce x Sb 2 series due to substitutional disorder.

Transport properties and crystal structure of layered LaSb2

“…3,4,8,9 Recently, evidence of a CDW transition was observed and hypothesized to arise from stacking faults. 11 In the present study, we have observed an isotropic resistivity in the layers of an orthorhombic crystal. While this is physically possible, then it is unlikely considering the range of temperature and magnetic fields used here.…”

“…The observed isotropy strongly suggests such mechanism to be at play. Furthermore, previous reports have also reported low crystal quality in the c-direction 6 and weak interlayer interaction, 3,4,[9][10][11] suggesting that this is a common feature of LaSb 2 crystals, especially when considering the good agreement between reported properties and RRRs. Another manifestation of the weak interaction between layers is that the irregularities between layers, be it twinning or stacking faults, has little to no influence on the in-plane crystallinity, which is evident from the high RRRs and long mean free path of the phonons and electrons.…”

“…The observed stability and slow change in amorphous contribution is in agreement with later reports, where no surface contamination was observed despite cleaving the crystals in air to allow for the removal of leftover loose flakes from the cleaving process. 4,11 These loose flakes could also be the reason for an earlier study not observing any diffraction spots in their Low Energy Electron Diffraction experiments. 3 The fact that LaSb 2 is stable enough to be handled and cleaved in air could be useful for obtaining very thin samples; however, the strong interaction between the layers, which is evident from termination having been observed at the pure antimony layer, 3 does make exfoliation difficult.…”

“…[12][13][14][15][16][17][18] LaAgSb 2 is another example that has a CDW state and a large magnetoresistance that shows no signs of saturation at 18 T. [19][20][21][22] This has led many to search for the presence of a CDW in LaSb 2 , and despite not observing direct evidence of a CDW, many still cite it as a likely explanation for the linear magnetoresistance. 3,4,[7][8][9] Evidence of a CDW transition was eventually observed in a solid solution with Ce and correlated to a kink in the resistivity that changes with Ce concentration, where the kink for pure LaSb 2 is at 355 K. 11 The authors hypothesized that the observed CDW arose due to stacking faults present in all their samples independent of Ce concentration.…”

“…4 The superconductivity and high linear magnetoresistance of LaSb 2 has inspired many studies. [3][4][5][6][7][8][9][10][11] The superconducting phase was originally reported to have a critical temperature of 0.4 K. 5 Later reports showed that the superconducting transition is broad and with an onset temperature up to 2.5 K in the a,b-plane and 1.0 K along the c-axis and achieving full superconductivity between 0.4 and 0.7 K. 4,9,10 The critical field is observed to be higher in-plane than out-of-plane. Applying a pressure results in a narrowing of the superconducting transition to near step-like with a critical temperature in and out-of-plane of 1.7 K, showing that pressure stabilizes the superconducting state and changes it from 2D to 3D behavior.…”