Phase diagram of URu _{2– x} Fe _x Si ₂ in high magnetic fields

Abstract

Electrical transport measurements were performed on URu 2−x FexSi 2 single-crystal specimens in high magnetic fields up to 45 T (DC fields) and 60 T (pulsed fields). We observed a systematic evolution of the critical fields for both the hidden-order (HO) and large-moment antiferromagnetic (LMAFM) phases and established the 3D phase diagram of T-H-x. In the HO phase, H/H 0 scales with T/T 0 and collapses onto a single curve. However, in the LMAFM phase, this single scaling relation is not satisfied. Within a certain range of x values, the HO phase reenters after the LMAFM phase is suppressed by the magnetic field, similar to the behavior observed for URu 2 Si 2 within a certain range of pressures.hidden order | URu 2 Si 2 | high magnetic field | phase diagram A prime example of emergent behavior in a strongly correlated electron system is the so-called "hidden-order" (HO) phase in the heavy fermion compound URu2Si2 that occurs below T0 = 17.5 K and coexists with superconductivity below Tc = 1.5 K (1-3). Neutron-scattering experiments reveal the presence of a small antiferromagnetic moment of only 0.03 µB /U parallel to the tetragonal c axis in the HO phase (4) which is far too small to account for the entropy of 0.2Rln(2) associated with the observed specific heat anomaly (2). Early attempts to identify the order parameter (OP) of the HO phase were unsuccessful, which led to the terminology of hidden order. Over the past three decades, experimentalists and theoreticians alike have expended an enormous amount of effort in trying to identify the OP of the elusive HO phase and many candidates for the HO phase have been proposed (5, 6). However, the nature and origin of the HO phase have not yet been definitively established, although some possibilities have recently emerged (7,8).An important aspect of the HO phase is that it exists in close proximity to a large-moment antiferromagnetic (LMAFM) phase that arises for pressures greater than Pc ≥ 0.5-1.5 GPa (9). Detailed neutron-diffraction experiments suggest that the small antiferromagnetic moment in the HO phase is not intrinsic but is induced by strain that leads to the presence of small regions of the LMAFM phase within the HO phase (10, 11). In addition, inelastic neutron-scattering experiments reveal that at Pc, the spin gap of the incommensurate Q1 = (0.4, 0, 0) resonance mode related to the heavy quasi-particles increases from 4 meV to 8 meV, while the spin gap of the commensurate Q0 = (1, 0, 0) resonance mode vanishes (12), demonstrating that the local spin degrees of freedom at Q0 "freeze out" above Pc and lead to the emergence of the LMAFM phase. This suggests that the HO and LMAFM phases are intimately related and that a detailed understanding of both phases and their competition will be useful in unraveling the nature of the OP of the HO phase.While experiments under applied pressure provide tantalizing clues regarding the relationship between HO and LMAFM order, progress has been slow due to experimental challenges associated with measurements under suc...

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

“…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.…”

Collinear antiferromagnetic order in URu2Si2−xPx revealed by neutron diffraction

“…In the Supplemental Material [68], we also provide a discussion of the effect of applied magnetic fields (with reference to the studies [83][84][85][86][87][88]). This is another tuning parameter that may serve to reveal similarities and differences between different ground states of URu 2 Si 2 derivatives.…”

Heat capacity of URu$_{2-x}$Os$_x$Si$_2$ at low temperatures

“…( 2). Earlier studies 1,24,25,34 have associated the product V 0 s(0) with the hybridization (and/or charge) gap. In our theory s(0) cannot possibly change with x or external pressure since its value is determined by a local matrix element.…”

“…[19][20][21][22] One type of such experiments involves the studies of alloys in which ruthenium (Ru) is substituted either with iron (Fe) or osmium (Os). [23][24][25] For example, the substitution of Ru with Os produces an effect of negative pressure leading to a predominantly isotropic lattice expansion. By contrasting the changes in the critical temperature T c with the changes in the Sommerfeld coefficient γ, one should (at least, in principle) be able to check whether this leads to a contradiction with either 'itinerant' or 'localized' theoretical models.…”