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تسجيل مستخدم جديدA signature of hidden order in URu2Si2 : the excitation at the wavevector Q0 = (100)
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Simultaneous neutron-scattering and thermal expansion measurements on the heavy-fermion superconductor URu2Si2 under hydrostatic pressure of 0.67 GPa have been performed in order to detect the successive paramagnetic, hidden order, and large moment antiferromagnetic phases on cooling. The temperature dependence of the sharp low energy excitation at the wavevector Q_0=(100) shows that this excitation is clearly a signature of the hidden order state. In the antiferromagnetic phase, this collective mode disappears. The higher energy excitation at the incommensurate wavevector Q_1=(1.4,0,0) persists in the antiferromagnetic phase but increases in energy. The collapse of the inelastic neutron scattering at Q_0 coincides with the previous observation of the disappearance of superconductivity.
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New inelastic neutron scattering experiments have been performed on URu2Si2 with special focus on the response at Q0=(1,0,0), which is a clear signature of the hidden order (HO) phase of the compound. With polarized inelastic neutron experiments, it
is clearly shown that below the HO temperature (T0 = 17.8 K) a collective excitation (the magnetic resonance at E0 approx 1.7 meV) as well as a magnetic continuum co-exist. Careful measurements of the temperature dependence of the resonance lead to the observation that its position shifts abruptly in temperature with an activation law governed by the partial gap opening and that its integrated intensity has a BCS-type temperature dependence. Discussion with respect to recent theoretical development is made.
Solids with strong electron correlations generally develop exotic phases of electron matter at low temperatures. Among such systems, the heavy-fermion semi-metal URu2Si2 presents an enigmatic transition at To = 17.5 K to a `hidden order state whose o
rder parameter remains unknown after 23 years of intense research. Various experiments point to the reconstruction and partial gapping of the Fermi surface when the hidden-order establishes. However, up to now, the question of how this transition affects the electronic spectrum at the Fermi surface has not been directly addressed by a spectroscopic probe. Here we show, using angle-resolved photoemission spectroscopy, that a band of heavy quasi-particles drops below the Fermi level upon the transition to the hidden-order state. Our data provide the first direct evidence of a large reorganization of the electronic structure across the Fermi surface of URu2Si2 occurring during this transition, and unveil a new kind of Fermi-surface instability in correlated electron systems
Since the 1985 discovery of the phase transition at $T_{rm HO}=17.5$ K in the heavy-fermion metal URu$_2$Si$_2$, neither symmetry change in the crystal structure nor magnetic ordering have been observed, which makes this hidden order enigmatic. Some
high-field experiments have suggested electronic nematicity which breaks fourfold rotational symmetry, but direct evidence has been lacking for its ground state at zero magnetic field. Here we report on the observation of lattice symmetry breaking from the fourfold tetragonal to twofold orthorhombic structure by high-resolution synchrotron X-ray diffraction measurements at zero field, which pins down the space symmetry of the order. Small orthorhombic symmetry-breaking distortion sets in at $T_{rm HO}$ with a jump, uncovering the weakly first-order nature of the hidden-order transition. This distortion is observed only in ultrapure sample, implying a highly unusual coupling nature between the electronic nematicity and underlying lattice.
In the hidden order of URu2Si2 the resistivity at very low temperature shows no T^2 behavior above the transition to superconductivity. However, when entering the antiferromagnetic phase, the Fermi liquid behavior is recovered. We discuss the change
of the inelastic term when entering the AF phase with pressure considering the temperature dependence of the Grueneisen parameter at ambient pressure and the influence of superconductivity by an extrapolation of high field data.
We report angle-resolved photoemission spectroscopy (ARPES) experiments probing deep into the hidden order (HO) state of URu2Si2, utilizing tunable photon energies with sufficient energy and momentum resolution to detect the near Fermi surface (FS) b
ehavior. Our results reveal: (i) the full itinerancy of the 5f electrons; (ii) the crucial three-dimensional (3D) k-space nature of the FS and its critical nesting vectors, in good comparison with density-functional theory calculations, and (iii) the existence of hot-spot lines and pairing of states at the FS, leading to FS gapping in the HO phase.
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