1,720,984 research outputs found
Relation between cuprate superconductivity and magnetism: A Raman study of (CaLa)1(BaLa)2Cu3 Oy
Full text linkWe present an investigation of charge-compensated antiferromagnetic (CaxLa1.x)(Ba1.75.xLa0.25+x)Cu3Oy
single crystals using Raman scattering as well as muon spin rotation. In this system the parameter x controls
the Cu-O-Cu superexchange interaction via bond distances and buckling angles. The oxygen content y controls
the charge doping. In the absence of doping the two-magnon peak position is directly proportional to the
superexchange strength J .We find that both x and y affect the peak position considerably. The N´eel temperature
determined from muon spin rotation on the same samples independently confirms the strong dependence of the
magnetic interaction on x and y. We find a considerable increase in the maximum superconducting transition
temperature T max
c with J . This is strong evidence of the importance of orbital overlap to superconductivity in this
family of cuprates.1551sciescopu
Lattice and orbital fluctuations in TiPO4
Full text linkIn the s = 1/2 antiferromagnetic spin chain material TiPO4, the formation of a spin gap takes place in a
two-step process with two characteristic temperatures, T
∗ = 111 K and TSP = 74 K. We observe an unusual
lattice dynamics over a large temperature regime as well as evidence for an orbital instability preceding the
spin-Peierls transition. We relate different intrachain exchange interactions of the high temperature compared
to the spin-Peierls phase to a modification of the orbital ordering pattern. In particular, our observation of a
high-energy excitation of mixed electronic and lattice origin suggests an exotic dimerization process different
from other spin-Peierls materials.1221sciescopu
Phase separation in iron chalcogenide superconductor Rb0.8+xFe1.6+ySe2 as seen by Raman light scattering and band structure calculations
No full textWe report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K over a wide temperature region 3-500 K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed RbδFe2Se2 (122) conductive phase. The superconducting gap with dx 2-y 2 symmetry has been detected in our spectra. In the range 0-600 cm-1 we observe a weak but highly polarized B1g-type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M0.8+xFe1.6+ySe2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic RbδFe2Se2 phase and the insulating Rb2Fe4Se5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb0.8+xFe1.6+ySe2. Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb2Fe4Se5phases. PACS: 78.30.-j Infrared and Raman spectra; 74.25.Jb Electronic structure (photoemission, etc.); 74.25.Kc Phonons; 74.70.Xa Pnictides and chalcogenides. © Yu. Pashkevich, V. Gnezdilov, P. Lemmens, T. Shevtsova, A. Gusev, K. Lamonova, D. Wulferding, S. Gnatchenko, E. Pomjakushina, and K. Conder, 2016 Published by AIP Publishing011sciescopu
Melting of Unidirectional Charge Density Waves across Twin Domain Boundaries in GdTe3
No full textSolids undergoing a transition from order to disorder experience a proliferation of topological defects. The melting process generates transient quantum states. However, their dynamic nature with a femtosecond lifetime hinders exploration with atomic precision. Here, we suggest an alternative approach to the dynamic melting process by focusing on the interface created by competing degenerate quantum states. We use a scanning tunneling microscope (STM) to visualize the unidirectional charge density wave (CDW) and its spatial progression (“static melting”) across a twin domain boundary (TDB) in the layered material GdTe3. Combining the STM with a spatial lock-in technique, we reveal that the order parameter amplitude attenuates with the formation of dislocations and thus two different unidirectional CDWs coexist near the TDB, reducing the CDW anisotropy. Notably, we discovered a correlation between this anisotropy and the CDW gap. Our study provides valuable insight into the behavior of topological defects and transient quantum states. © 2023 American Chemical Society.11Nsciescopu
One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet
No full textThe spin-1/2 antiferromagnetic Heisenberg model on a kagome lattice is geometrically frustrated, which is expected to promote the formation of many-body quantum entangled states. The most sought-after among these is the quantum spin-liquid phase, but magnetic analogues of liquid, solid and supersolid phases may also occur, producing fractional plateaus in the magnetization. Here, we investigate the experimental realization of these predicted phases in the kagome material YCu3(OD)6+xBr3−x (x ≈ 0.5). By combining thermodynamic and Raman spectroscopic techniques, we provide evidence for fractionalized spinon excitations and observe the emergence of a 1/9 magnetization plateau. These observations establish YCu3(OD)6+xBr3−x as a model material for exploring the 1/9 plateau phase. © 2024, The Author(s), under exclusive licence to Springer Nature Limited.11Nsciescopu
Experimental signatures of nodeless multiband superconductivity in a 2H-Pd 0.08 TaSe 2 single crystal
No full textAbstract In order to understand the superconducting gap nature of a 2H-Pd 0.08 TaSe 2 single crystal with T c = 3.13 K , in-plane thermal conductivity κ , in-plane London penetration depth λ L , and the upper critical fields H c 2 have been investigated. At zero magnetic field, it is found that no residual linear term κ 0 / T exists and λ L follows a power-law T n (T: temperature) with n = 2.66 at T ≤ 1 3 T c , supporting nodeless superconductivity. Moreover, the magnetic-field dependence of κ 0 /T clearly shows a shoulder-like feature at a low field region. The temperature dependent H c 2 curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near T c , consistent with the shape predicted by the two-band theory and the anisotropy ratio between the H c 2 (T) curves exhibits strong temperature-dependence. All these results coherently suggest that 2H-Pd 0.08 TaSe 2 is a nodeless, multiband superconductor
Direct observation of the M2 phase with its Mott transition in a VO2 film
No full textIn VO2, the explicit origin of the insulator-to-metal transition is still disputable between Peierls and Mott insulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerized vanadium ions. However, the origin of the M2 phase is still obscure. Here, we study a granular VO2 film using conductive atomic force microscopy and Raman scattering. Upon the structural transition from monoclinic to rutile, we observe directly an intermediate state showing the coexistence of monoclinic M1 and M2 phases. The conductivity near the grain boundary in this regime is six times larger than that of the grain core, producing a donut-like landscape. Our results reveal an intra-grain percolation process, indicating that VO2 with the M2 phase is a Mott insulator. © 2016 Author(s6
Linear scaling relationship of N\'{e}el temperature and dominant magnons in pyrochlore ruthenates
Full text linkWe present a systematic Raman spectroscopy study on a series of pyrochlore
ruthenates, a system which is not yet clearly settled on its magnetic origin
and structure. Apart from the Raman-active phonon modes, new peaks that appear
in the energy range of 15 - 35 meV below the N\'{e}el temperature are assigned
as one-magnon modes. The temperature evolution of one-magnon modes displays no
significant thermal dependence in mode frequencies while the intensities
decrease monotonically. Remarkably, one-magnons from all compounds show similar
characteristics with a single dominant peak at lower energy and weaker side
peaks at a couple of meV higher energy. Most importantly, we uncover a striking
proportionality between the dominant magnon mode energies and the N\'{e}el
temperature values. Our results suggest the Ru ions may have similar or the
same magnetic phase in all pyrochlore ruthenates of our study. We have thus
found an avenue for directly tuning the magnetic exchange interaction by the
selection of the -site ion
Spatially resolved penetration depth measurements and vortex manipulation in the ferromagnetic superconductor ErNi2 B2 C
Full text linkWe present a local probe study of the magnetic superconductor ErNi2B2C, using magnetic force microscopy at sub-Kelvin temperatures. ErNi2B2C is an ideal system to explore the effects of concomitant superconductivity and ferromagnetism. At 500 mK, far below the transition to a weakly ferromagnetic state, we directly observe a structured magnetic background on the micrometer scale. We determine spatially resolved absolute values of the magnetic penetration depth λ and study its temperature dependence as the system undergoes magnetic phase transitions from paramagnetic to antiferromagnetic, and to weak ferromagnetic, all within the superconducting regime. In addition, we estimate the absolute pinning force of Abrikosov vortices, which shows a position dependence and temperature dependence as well, and discuss the possibility of the purported spontaneous vortex formation. © 2015 American Physical Society. ©2015 American Physical Society1551sciescopu
- …
