Nematic domains and resistivity in an itinerant metamagnet coupled to a lattice

The nature of the emergent phase near a putative quantum critical point in the bilayer ruthenate Sr$_3$Ru$_2$O$_7$ has been a recent subject of intensive research. It has been suggested that this phase may possess electronic nematic order(ENO). In this work, we investigate the possibility of nematic domain formation in the emergent phase, using a phenomenological model of electrons with ENO and its coupling to lattice degrees of freedom. The resistivity due to the scattering off the domain walls is shown to closely follow the ENO parameter. Our results provide qualitative explanations for the dependence of the resistivity on external magnetic fields in Sr$_3$Ru$_2$O$_7$.Comment: 4 pages, 4 figures, published versio

Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization and 79Br NQR - 125Te NMR

We present high-field magnetization and $^{79}$Br nuclear quadrupole resonance (NQR) and $^{125}$Te nuclear magnetic resonance (NMR) studies in the weakly coupled Cu$^{2+}$ ($S=1/2$) tetrahedral system Cu$_2$Te$_2$O$_5$Br$_2$. The field-induced level crossing effects were observed by the magnetization measurements in a long-ranged magnetically ordered state which was confirmed by a strong divergence of the spin-lattice relaxation rate 1/T1 at T0=13.5 K. In the paramagnetic state, 1/T1 reveals an effective singlet-triplet spin gap much larger than that observed by static bulk measurements. Our results imply that the inter- and the intra-tetrahedral interactions compete, but at the same time they cooperate strengthening effectively the local intratetrahedral exchange couplings. We discuss that the unusual feature originates from the frustrated intertetrahedral interactions.Comment: 5 pages, 4 figures, accepted in Phys. Rev. B as a Rapid Communication

Critical Current of the Spin-Triplet Superconducting Phase in Sr2_2RuO4_4

There have been two different proposals for the spin-triplet order parameter of the superconducting phase in Sr$_2$RuO$_4$; an $f$-wave order parameter and the multigap model where some of the bands have the line node. In an effort to propose an experiment that can distinguish two cases, we study the behavior of the supercurrent and compute the critical current for these order parameters when the sample is a thin film with the thickness $d \ll \xi$ where $\xi$ is the coherence length. It is found that the supercurrent behaves very differently in two models. This will serve as a sharp test for the identification of the correct order parameter.Comment: 4 pages, 1 figur

Universal scaling in sports ranking

Ranking is a ubiquitous phenomenon in the human society. By clicking the web pages of Forbes, you may find all kinds of rankings, such as world's most powerful people, world's richest people, top-paid tennis stars, and so on and so forth. Herewith, we study a specific kind, sports ranking systems in which players' scores and prize money are calculated based on their performances in attending various tournaments. A typical example is tennis. It is found that the distributions of both scores and prize money follow universal power laws, with exponents nearly identical for most sports fields. In order to understand the origin of this universal scaling we focus on the tennis ranking systems. By checking the data we find that, for any pair of players, the probability that the higher-ranked player will top the lower-ranked opponent is proportional to the rank difference between the pair. Such a dependence can be well fitted to a sigmoidal function. By using this feature, we propose a simple toy model which can simulate the competition of players in different tournaments. The simulations yield results consistent with the empirical findings. Extensive studies indicate the model is robust with respect to the modifications of the minor parts.Comment: 8 pages, 7 figure

Biaxial spin-nematic phase of two dimensional disordered rotor models and spin-one bosons in optical lattices

We show that the ground state of disordered rotor models with quadrupolar interactions can exhibit biaxial nematic ordering in the disorder-averaged sense. We present a mean-field analysis of the model and demonstrate that the biaxial phase is stable against small quantum fluctuations. We point out the possibility of experimental realization of such rotor models using ultracold spin-one Bose atoms in a spin-dependent and disordered optical lattice in the limit of a large number of atoms per site and also suggest an imaging experiment to detect the biaxial nematicity in such systems.Comment: revtex file 7 pages, 2 figures, version published in PR

Transdiagnostic treatment of bipolar disorder and comorbid anxiety using the Unified Protocol for Emotional Disorders: A pilot feasibility and acceptability trial

BACKGROUND Comorbid anxiety in bipolar disorder (BD) is associated with greater illness severity, reduced treatment response, and greater impairment. Treating anxiety in the context of BD is crucial for improving illness course and outcomes. The current study examined the feasibility, acceptability and preliminary efficacy of the Unified Protocol (UP), a transdiagnostic cognitive behavioral therapy, as an adjunctive treatment to pharmacotherapy for BD and comorbid anxiety disorders. METHODS Twenty-nine patients with BD and at least one comorbid anxiety disorder were randomized to pharmacotherapy treatment-as-usual (TAU) or TAU with 18 sessions of the UP (UP+TAU). All patients completed assessments every four weeks to track symptoms, functioning, emotion regulation and temperament. Linear mixed-model regressions were conducted to track symptom changes over time and to examine the relationship between emotion-related variables and treatment response. RESULTS Satisfaction ratings were equivalent for both treatment groups. Patients in the UP+TAU group evidenced significantly greater reductions over time in anxiety and depression symptoms (Cohen's d's>0.80). Baseline levels of neuroticism, perceived affective control, and emotion regulation ability predicted magnitude of symptom change for the UP+TAU group only. Greater change in perceived control of emotions and emotion regulation skills predicted greater change in anxiety related symptoms. LIMITATIONS This was a pilot feasibility and acceptability trial; results should be interpreted with caution. CONCLUSIONS Treatment with the UP+TAU was rated high in patient satisfaction, and resulted in significantly greater improvement on indices of anxiety and depression relative to TAU. This suggests that the UP may be a feasible treatment approach for BD with comorbid anxiety.This work was supported by a Postdoctoral National Research Service Award from the National Institutes of Health [F32 MH098490] to K. Ellard. (F32 MH098490 - Postdoctoral National Research Service Award from the National Institutes of Health)Accepted manuscrip

Collective modes and sound propagation in a p-wave superconductor: Sr2_2RuO4_4

There are five distinct collective modes in the recently discovered p-wave superconductor Sr$_2$RuO$_4$; phase and amplitude modes of the order parameter, clapping mode (real and imaginary), and spin wave. The first two modes also exist in the ordinary s-wave superconductors, while the clapping mode with the energy $\sqrt{2} \Delta(T)$ is unique to Sr$_2$RuO$_4$ and couples to the sound wave. Here we report a theoretical study of the sound propagation in a two dimensional p-wave superconductor. We identified the clapping mode and study its effects on the longitudinal and transverse sound velocities in the superconducting state. In contrast to the case of $^3$He, there is no resonance absorption associated with the collective mode, since in metals $\omega/(v_F |{\bf q}|) \ll 1$, where $v_F$ is the Fermi velocity, {\bf q} is the wave vector, and $\omega$ is the frequency of the sound wave. However, the velocity change in the collisionless limit gets modified by the contribution from the coupling to the clapping mode. We compute this contribution and comment on the visibility of the effect. In the diffusive limit, the contribution from the collective mode turns out to be negligible. The behaviors of the sound velocity change and the attenuation coefficient near $T_c$ in the diffusive limit are calculated and compared with the existing experimental data wherever it is possible. We also present the results for the attenuation coefficients in both of the collisionless and diffusive limits at finite temperatures.Comment: RevTex, 12 pages, 2 figures, Replaced by the published versio