Strong increase in ultrasound attenuation below T2 in Sr2RuO4 : possible evidence for domains

Funding information: B.J.R. and S.G. acknowledge support from the Office of Basic Energy Sciences of the U.S. Department of Energy under award No. DE-SC0020143. B.J.R. and S.G. acknowledge support from the Cornell Center for Materials Research with funding from the Materials Research Science and Engineering Centers program of the National Science Foundation (cooperative agreement No. DMR-1719875). T.G.K. acknowledges support from the National Science Foundation under Grant No. PHY-2110250. N.K. acknowledges support from Japan Society for the Promotion of Science (JSPS) KAKENHI (Grants No. JP17H06136, No. JP18K04715, and No. 21H01033) and Japan Science and Technology Agency Mirai Program (JPMJMI18A3) in Japan.Recent experiments suggest that Sr2RuO4 has a two-component superconducting order parameter (OP). A two-component OP has multiple degrees of freedom in the superconducting state that can result in low-energy collective modes or the formation of domain walls—a possibility that would explain a number of experimental observations including the smallness of the signature of time reversal symmetry breaking at Tc and telegraph noise in critical current experiments. We use resonant ultrasound spectroscopy to perform ultrasound attenuation measurements across the superconducting Tc of Sr2RuO4. We find that compressional sound attenuation increases by a factor of 7 immediately below Tc , in sharp contrast with what is found in both conventional (s-wave) and high-Tc (d-wave) superconductors. Our observations are most consistent with the presence of domain walls that separate different configurations of the superconducting OP. The fact that we only observe an increase in sound attenuation for compressional strains, and not for shear strains, suggests an inhomogeneous superconducting state formed of two distinct, accidentally degenerate superconducting OPs that are not related to each other by symmetry. Whatever the mechanism, a factor of 7 increase in sound attenuation is a singular characteristic that must be reconciled with any potential theory of superconductivity in Sr2RuO4.Publisher PDFPeer reviewe

Topological metamagnetism : thermodynamics and dynamics of the transition in spin ice under uniaxial compression

This work was carried out within the framework of a Max-Planck independent research group on strongly correlated systems. We acknowledge financial support from the Deutsche Forschungsgemeinschaft through SFB 1143 (Project No. 247310070) and Cluster of Excellence ct.qmat (EXC 2147, Project No. 390858490), EPSRC (EP/T028637/1), ShanghaiTech University, Agencia Nacional de Promoción Científica y Tecnológica through PICT 2017-2347, and Consejo Nacional de Investigaciones Científicas y Técnicas through PIP 0446.Metamagnetic transitions are analogs of a pressure-driven gas-liquid transition in water. In insulators, they are marked by a superlinear increase in the magnetization that occurs at a field strength set by the spin exchange interactions. Here we study topological metamagnets, in which the magnetization is itself a topological quantity and for which we find a single transition line for two materials with substantially different magnetic interactions: the spin ices Dy2Ti2O7 and Ho2Ti2O7. We study single crystals under magnetic field and stress applied along the [001] direction and show that this transition, of the Kasteleyn type, has a magnetization versus field curve with upward convexity and a distinctive asymmetric peak in the susceptibility. We also show that the dynamical response of Ho2Ti2O7 is sensitive to changes in the Ho3+ environment induced by compression along [001]. Uniaxial compression may open up experimental access to equilibrium properties of spin ice at lower temperatures.Publisher PDFPeer reviewe

High sensitivity heat capacity measurements on Sr2RuO4 under uniaxial pressure

Funding: Parts of this work were funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - TRR 288 -422213477 (projects A10 and B01). NK acknowledges the support from JSPS KAKENHI (nos. JP17H06136 and JP18K04715) and JST-Mirai Program (no. JPMJMI18A3) in Japan and YM from JSPS KAKENHI (nos. JP15H05852, JP15K21717) and JSPS core-to-core programme. YSL acknowledges the support of a St Leonard’s scholarship from the University of St Andrews, the Engineering and Physical Sciences Research Council via the Scottish Condensed Matter Centre for Doctoral Training under grant EP/G03673X/1, and the Max Planck Society.A key question regarding the unconventional superconductivity of Sr2RuO4 remains whether the order parameter is single- or two-component. Under a hypothesis of two-component superconductivity, uniaxial pressure is expected to lift their degeneracy, resulting in a split transition. The most direct and fundamental probe of a split transition is heat capacity. Here, we report development of new high-frequency methodology for measurement of heat capacity of samples subject to large and highly homogeneous uniaxial pressure. We place an upper limit on the heat capacity signature of any second transition of a few per cent of the primary superconducting transition. The normalized jump in heat capacity, Δ C/C, grows smoothly as a function of uniaxial pressure, but we find no qualitative evidence of a pressure-induced order parameter transition. Thanks to the high precision of our measurements, these findings place stringent constraints on theories of the superconductivity of Sr2RuO4.PostprintPeer reviewe

Kazalo

The superconducting state in the quasi-two-dimensional and strongly correlated Sr$_2$RuO$_4$ is uniquely held up as a solid state analog to superfluid $^3$He-$A$, with an odd-parity order parameter that also breaks time reversal symmetry, and for which the vector order parameter has the same direction in spin space for all electron momenta. The recent discovery that uniaxial pressure causes a steep rise and maximum in transition temperature ($T_c$) in strained samples motivated the study of $^{17}$O nuclear magnetic resonance (NMR) that we describe in this article. A reduction of Knight shifts $K$ was observed for all strain values and temperatures $T<T_c$, consistent with a drop in spin polarization in the superconducting state. In unstrained samples, our results are in contradiction with a body of previous NMR work, and with the most prominent previous proposals for the order parameter of Sr$_2$RuO$_4$. Possible alternative scenarios are discussed.Comment: Manuscript: 4 figures, 2 tables; Supplementary Information: 5 figure

HIGH-RESOLUTION LASER PHOTOACOUSTIC SPECTROSCOPY OF PH3PH_{3} : THE FIFTH P-H STRETCHING OVERTONE BANDS.

Author Institution: Laboratoire de Physique des Lasers; Universite de Lille; Anorganische ChemieA titanium:sapphire ring laser (Coherent $899-29$) pumped by an Innova 400, 15 W argon-ion laser was coupled to a high sensitivity acoustic cell $(\alpha_{min} = 5\times10^{-9} cm^{-1})$ filled with $PH_{3}$. The cell is an acoustic resonator built from stainless steel pipe (10 cm length, i.d. 6 mm) and equipped with two buffer volumes of 5 cm at both ends in order to reduce the ambient noise. The laser beam was chopped at 1370 Hz for exciting the first longitudinal mode of the resonator. The photoacoustic signal was detected by two electret microphones (Knowles EK-3024) mounted on a summing amplifier circuit and converted to a DC voltage by a lock -in-amplifier. Most spectra were recorded with a laser power of 1.5 W and using a time constant of 300 ms, with a typical sensitivity of $100-500 \mu V$. The spectrum of phosphine has been recorded at room temperature with a gas pressure of 116 hPa between 12 500 and $12 780 cm^{-1}$. The $\Delta v=6$ spectrum is characterized by one band system centered at $12 678 cm^{-1}$. It is assigned to the local mode P-H stretching $(600 A_{1}/E)$ bands. The analysis started by locating the most intense $^{r}P_{k}(J)$ and $^{p}P_{k}(J)$ lines (with K=J) and the $^{r}Q_{0}(J)$ lines of the perpendicular band, using the ground state combination differences technique. Forty-four lines associated with J, K = 0-9, 0-9 have been assigned up to now. For the weak parallel band, only 11 lines up to J=4 have been assigned. The lines have been fitted with a Hamiltonian model which makes use of simple arithmetic relations between some rovibrational parameters (H. Buerger, M. Lecoutre, T.R. Huet, J. Breidung, W. Thiel, V. Hanninen and L. Halonen, J. Chem. Phys. 114 (2001) 8844, and Ref. therein). The program written by L. Halonen was used (L. Halonen, private communication). The ground state constants were kept fixed to the values from the litterature (L. Fusina and G. Di Lonardo, J. Mol. Struct. 517-518 (2000) 67-78). No perturbation was observed at this stage of the analysis. The molecular parameters seem to confirm the local mode tendency of the $PH_{3}$ molecule in the near infrared range. This work is supported by the EU Commission (Research Training Network No. HPRN-CT-2000-00022)