arXiv subjects

E. L. Green

Publications and source records attributed to E. L. Green.

10 recordsLinked to original sources

arXiv2022

Martensitic transformation in V_3Si single crystal: ^51V NMR evidence for coexistence of cubic and tetragonal phases

The Martensitic transformation (MT) in A15 binary-alloy superconductor V_3Si, though studied extensively, has not yet been conclusively linked with a transition to superconductivity. Previous NMR studies have mainly been on powder samples and with little emphasis on temperature dependence during the transformation. Here we study a high-quality single crystal, where quadrupolar splitting of NMR spectra for ^51V allowed us to distinguish between spectra from transverse chains of V as a function of temperature. Our data revealed that (1) the MT is not abrupt, but rather there is a microscopic coexistence of pre-transformed cubic phase and transformed tetragonal phase over a few K below and above Tm, while (2) no pre-transformed phase can be found at Tc, and (3) the Martensitic lengthening of one axis occurs predominantly in a plane perpendicular to the crystal growth axis, as twinned domains.

cond-mat.supr-con↗

arXiv2019

Fermi-surface topology of the heavy-fermion system Ce$_{2}$PtIn$_{8}$

Ce$_{2}$PtIn$_{8}$ is a recently discovered heavy-fermion system structurally related to the well-studied superconductor CeCoIn$_{5}$. Here, we report on low-temperature de Haas-van Alphen-effect measurements in high magnetic fields in Ce$_{2}$PtIn$_{8}$ and Pr$_{2}$PtIn$_{8}$. In addition, we performed band-structure calculations for localized and itinerant Ce-$4f$ electrons in Ce$_{2}$PtIn$_{8}$. Comparison with the experimental data of Ce$_{2}$PtIn$_{8}$ and of the $4f$-localized Pr$_{2}$PtIn$_{8}$ suggests the itinerant character of the Ce-$4f$ electrons. This conclusion is further supported by the observation of effective masses in Ce$_{2}$PtIn$_{8}$, which are strongly enhanced with up to 26 bare electron masses.

cond-mat.str-el↗

arXiv2018

Fermi surface reconstruction and dimensional topology change in Nd-doped CeCoIn$_5$

We performed low-temperature de Haas-van Alphen (dHvA) effect measurements on a Ce$_{1-x}$Nd$_x$CoIn$_5$ series, for x = 0.02, 0.05, 0.1, and 1, down to T = 40 mK using torque magnetometry in magnetic felds up to 35 T. Our results indicate that a Fermi-surface (FS) reconstruction occurs from a quasi-two-dimensional (2D) topology for Nd-2% to a rather three-dimensional (3D) for Nd-5%, thus reducing the possibility of perfect FS nesting. The FS evolves further with increasing Nd content with no observed divergence of the effective mass between Nd-2% and 10%, consistent with the crossing of a spin density wave (SDW) type of quantum critical point (QCP). Our results elucidate the origin of the Q-phase observed at the 5% Nd-doping level [Raymond et al., J. Phys. Soc. Jpn. 83, 013707 (2014)].

cond-mat.str-el↗

arXiv2015

Acoustic signatures of the phases and phase transitions in Yb$_2$Ti$_2$O$_7$

We report on measurements of the sound velocity and attenuation in a single crystal of the candidate quantum- spin-ice material Yb$_2$Ti$_2$O$_7$ as a function of temperature and magnetic field. The acoustic modes couple to the spins magneto-elastically and, hence, carry information about the spin correlations that sheds light on the intricate magnetic phase diagram of Yb$_2$Ti$_2$O$_7$ and the nature of spin dynamics in the material. Particularly, we find a pronounced thermal hysteresis in the acoustic data with a concomitant peak in the specific heat indicating a possible first-order phase transition at about $0.17$ K. At low temperatures, the acoustic response to magnetic field saturates hinting at the development of magnetic order. Furthermore, mean-field calculations suggest that Yb$_2$Ti$_2$O$_7$ undergoes a first-order phase transition from a cooperative paramagnetic phase to a ferromagnet below $T\approx 0.17$ K.

cond-mat.str-el↗

arXiv2013

Evidence of d-wave Superconductivity in K_(1-x)Na_xFe_2As_2 (x = 0, 0.1) Single Crystals from Low-Temperature Specific Heat Measurements

From the measurement and analysis of the specific heat of high-quality K_(1-x)Na_xFe_2As_2 single crystals we establish the presence of large T^2 contributions with coefficients alpha_sc ~ 30 mJ/mol K^3 at low-T for both x=0 and 0.1. Together with the observed square root field behavior of the specific heat in the superconducting state both findings evidence d-wave superconductivity on almost all Fermi surface sheets with an average gap amplitude of Delta_0 in the range of 0.4 - 0.8 meV. The derived Delta_0 and the observed T_c agree well with the values calculated within the Eliashberg theory, adopting a spin-fluctuation mediated pairing in the intermediate coupling regime.

cond-mat.supr-con↗

arXiv2010

Distinct high-T transitions in underdoped Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$

In contrast to the simultaneous structural and magnetic first order phase transition $T_{0}$ previously reported, our detailed investigation on an underdoped Ba$_{0.84}$K$_{0.16}$Fe$_{2}$As$_{2}$ single crystal unambiguously revealed that the transitions are not concomitant. The tetragonal ($τ$: I4/mmm) - orthorhombic ($\vartheta$: Fmmm) structural transition occurs at $T_{S}\simeq$ 110 K, followed by an adjacent antiferromagnetic (AFM) transition at $T_{N}\simeq$ 102 K. Hysteresis and coexistence of the $τ$ and $\vartheta$ phases over a finite temperature range observed in our NMR experiments confirm the first order character of the structural transition and provide evidence that both $T_{S}$ and $T_{N}$ are strongly correlated. Our data also show that superconductivity (SC) develops in the $\vartheta$ phase below $T_{c}$ = 20 K and coexists with long range AFM. This new observation, $T_{S}\neq T_{N}$, firmly establishes another similarity between the hole-doped BaFe$_{2}$As$_{2}$ via K substitution and the electron-doped iron-arsenide superconductors.

cond-mat.supr-con↗

arXiv2004

Finite Hochschild cohomology without finite global dimension

Dieter Happel asked the following question: If the $n$-th Hochschild cohomology group of a finite dimensional algebra $Γ$ over a field vanishes for all sufficiently large $n$, is the global dimension of $Γ$ finite? We give a negative answer to this question.

math.KT↗

arXiv2004

Representation theory of the Drinfel'd doubles of a family of Hopf algebras

We investigate the Drinfel'd doubles $D(Λ_{n,d})$ of a certain family of Hopf algebras. We determine their simple modules and their indecomposable projective modules, and we obtain a presentation by quiver and relations of these Drinfel'd doubles, from which we deduce properties of their representations, including the Auslander-Reiten quivers of the $D(Λ_{n,d})$. We then determine decompositions of the tensor products of most of the representations described, and in particular give a complete description of the tensor product of two simple modules. This study also leads to explicit examples of Hopf bimodules over the original Hopf algebras.

math.RT↗

arXiv2004

Resolutions over Koszul algebras

In this paper we show that if $Λ=\amalg_{i\geq 0}Λ_i$ is a Koszul algebra with $Λ_0$ isomorphic to a product of copies of a field, then the minimal projective resolution of $Λ_0$ as a right $Λ$-module provides all the information necessary to construct both a minimal projective resolution of $Λ_0$ as a left $Λ$-module and a minimal projective resolution of $Λ$ as a right module over the enveloping algebra of $Λ$. The main tool for this is showing that there is a comultiplicative structure on a minimal projective resolution of $Λ_0$ as a right $Λ$-module.

math.RA↗

arXiv2004

The Hochschild cohomology ring modulo nilpotence of a monomial algebra

For a finite dimensional monomial algebra $Λ$ over a field $K$ we show that the Hochschild cohomology ring of $Λ$ modulo the ideal generated by homogeneous nilpotent elements is a commutative finitely generated $K$-algebra of Krull dimension at most one. This was conjectured to be true for any finite dimensional algebra over a field by Snashall-Solberg.

math.KT↗