Unfolding the physics of URu2Si2 through silicon to phosphorus substitution

Abstract

The heavy fermion intermetallic compound URu2Si2 exhibits a hidden-order phase below the temperature of 17.5 K, which supports both anomalous metallic behavior and unconventional superconductivity. While these individual phenomena have been investigated in detail, it remains unclear how they are related to each other and to what extent uranium f-electron valence fluctuations influence each one. Here we use ligand site substituted URu2Si2-xPx to establish their evolution under electronic tuning. We find that while hidden order is monotonically suppressed and destroyed for x≤0.035, the superconducting strength evolves non-monotonically with a maximum near x≈0.01 and that superconductivity is destroyed near x≈0.028. This behavior reveals that hidden order depends strongly on tuning outside of the U f-electron shells. It also suggests that while hidden order provides an environment for superconductivity and anomalous metallic behavior, it's fluctuations may not be solely responsible for their progression.

Single Crystal Growth of URu2Si2 by the Modified Bridgman Technique

“…Single-crystal X-ray diffraction measurements revealed the expected ThCr 2 Si 2 type structure with lattice constants a U = 4.133 (3) Å and c U = 9.58 (1) Å and a Th = 4.189 (2) Å and c Th = 9.745 (6) Å for URu 2 Si 2 and ThCr 2 Si 2 , respectively. These values are similar to those reported earlier [1][2][3][4]16,26]. For both materials, the direction perpendicular to the crystal surface is the c-axis, in agreement with earlier results from molten indium flux growth of URu 2 Si 2 ( Figure 1f) [16].…”

“…These values are similar to those reported earlier [1][2][3][4]16,26]. For both materials, the direction perpendicular to the crystal surface is the c-axis, in agreement with earlier results from molten indium flux growth of URu 2 Si 2 ( Figure 1f) [16]. Energy dispersive spectroscopy (EDS) measurements further confirm the expected URu 2 Si 2 and ThRu 2 Si 2 stoichiometry.…”

“…Elemental U, Th, Ru, Si, and In were sealed in the ratio 1:2:2:22 inside a tantalum crucible using a standard arc-furnace under argon gas. This is similar to what was reported previously for molten metal flux growth of URu 2 Si 2 in a resistive furnace [5,16]. The ampoule had an outer diameter of 1.01 cm, an inner diameter of 0.76 cm, and a length of 5 cm.…”

“…This is essential for the exploration of chemical substitution on the Si site, where unexplored possibilities include high vapor pressure elements such as Si → Sn, P, As, S, Se, and Te. Such work is attractive, as evidenced by recent studies of Si → P in URu 2 Si 2 that have uncovered a fascinating phase diagram featuring an unusual disconnect between hidden order and magnetism [16]. We also expect that our technique will be useful for the production of single crystals of the related materials UT 2 X 2 (T = transition metal and X = Si and Ge) [24].…”

“…This is an important advance in crystal growth for these materials, because it provides an alternative way to produce single crystals that are needed for a variety of experiments: e.g., not only is it possible to cleave them, but their quality is also high enough to observe quantum oscillations, as seen in other specimens of similar quality [16,17]. Furthermore, previous studies of URu 2 Si 2 have benefitted from investigation of chemical substitution series [16,[18][19][20][21][22][23]. Most such work has focused on the substitution of elements with low vapor pressures that are easily dissolved in a stoichiometric melt.…”