Evolution of critical pressure with increasing Fe substitution in the heavy-fermion systemURu2−xFexSi2

Abstract

Measurements of electrical resistivity, ρ(T ), were performed under quasi-hydrostatic pressure up to P ∼ 2.2 GPa to determine the pressure dependence of the so called "hidden order" (HO) and largemoment antiferromagnetic (LMAFM) phases for the URu2−xFexSi2 system with x = 0.025, 0.05, 0.10, 0.15, and 0.20. As the Fe concentration (x) is increased, we observed that a smaller amount of external pressure, Pc, is required to induce the HO → LMAFM phase transition. A critical pressure of Pc ∼ 1.2 GPa at x = 0.025 reduces to Pc ∼ 0 at x = 0.15, suggesting the URu2−xFexSi2 system is fully expressed in the LMAFM phase for x ≥ x * c = 0.15, where x * c denotes the ambient pressure critical concentration of Fe. Using a bulk modulus calculation to convert x to chemical pressure, P ch (x), we consistently found that the induced HO → LMAFM phase transition occurred at various combinations of xc and Pc such that P ch (xc) + Pc ≈ 1.5 GPa, where xc denotes those critical concentrations of Fe that induce the HO → LMAFM phase transition for the URu2−xFexSi2 compounds under pressure. We performed exponential fits of ρ(T ) in the HO and LMAFM phases in order to determine the pressure dependence of the energy gap, ∆, that opens over part of the Fermi surface in the transition from the paramagnetic (PM) phase to the HO/LMAFM phase at the transition temperature, T0. The change in the pressure variation of ∆(P ) at the HO → LMAFM phase transition is consistent with the values of Pc determined from the T0(P ) phase lines at the PM → HO/LMAFM transition.

Phase diagram of URu 2– x Fe x Si 2 in high magnetic fields

“…However, we did not observe a signature of the phase transition from the LMAFM to the HO phase. This may be consistent with the scenario of adiabatic continuity between the HO and LMAFM phases reported previously under 1.1 GPa (23), given that x = 0.12 converts to a similar chemical pressure (13)(14)(15). Fig.…”

“…The H0 for the LMAFM phase increases a lot faster, from 16.7 T for x = 0.15 to 33 T for x = 0.3. For comparison, we also plot H0 as a function of applied pressure (24) (top axis), with a conversion of ∆x/∆P = 0.1 GPa −1 that has been reported previously (13,14). The two sets of data match quite well in the HO range.…”

“…For example, many methods that are suitable for studying the electronic structure, such as angle-resolved photoemission spectroscopy, scanning tunneling microscopy, quantum oscillations, or highmagnetic-field electrical and thermal transport measurements, are difficult and, in some cases, probably impossible to carry out under high pressure. In recent studies, we demonstrated that tuning URu2Si2 by chemical substitution of Fe for Ru affords an opportunity to study the competition between the HO and LMAFM phases at ambient pressure (13)(14)(15). Notably, the substitution of the smaller Fe ions for Ru ions in URu2Si2 apparently acts as a "chemical pressure" and reproduces the general features of the temperature vs. pressure phase diagram, as demonstrated by electrical resistivity, magnetization, heat capacity, and thermal expansion measurements.…”

From hidden order to antiferromagnetism: Electronic structure changes in Fe-doped URu 2 Si 2

“…The electrical resistivity ρ(T ) measurements in the vicinity of the transition temperature for the single crystal samples of URu 1−x Fe x Si 2 with x = 0, 0.1 and 0.2 are shown in Refs. [37] and [48] However, there is a certain amount of broadening of the transition, which is to be expected with an increase in Fe concentration. Here, the larger concentrations of Fe that are introduced into the melts grown by the Czochralski method can result in a larger degree of inhomogeneity within the sample, especially in the direction of the vertical axis of the rod-shaped boule that is pulled from the melt.…”

“…The single crystals of Fe-substituted URu 2 Si 2 on which the ARPES measurements were made were grown by the Czochralski method in a tetra-arc furnace at UCSD. These crystals were characterized at UCSD by means of X-ray diffraction, electrical resistivity, magnetization, specific heat, and thermal expansion measurements as a function of temperature, magnetic field and pressure as described in several publications [37,48,49]. The electrical resistivity measurements were performed using a home-built probe in a liquid 4He Dewar by means of a standard four-wire technique at 16 Hz, using a Linear Research LR700 a.c. resistance bridge.…”