Search results for "Condensed Matter::Strongly Correlated Electrons"
showing 10 items of 888 documents
Electron refrigeration in hybrid structures with spin-split superconductors
2017
Electron tunneling between superconductors and normal metals has been used for an efficient refrigeration of electrons in the latter. Such cooling is a nonlinear effect and usually requires a large voltage. Here we study the electron cooling in heterostructures based on superconductors with a spin-splitting field coupled to normal metals via spin-filtering barriers. The cooling power shows a linear term in the applied voltage. This improves the coefficient of performance of electron refrigeration in the normal metal by shifting its optimum cooling to lower voltage, and also allows for cooling the spin-split superconductor by reverting the sign of the voltage. We also show how tunnel couplin…
Large enhancement of spin pumping due to the surface bound states in normal metal/superconductor structures
2020
We show that the spin pumping from ferromagnetic insulator into the adjacent metallic spin sink can be strongly stimulated by the superconducting correlations. The key physical mechanism responsible for this effect is the presence of Andreev bound states at the ferromagnetic insulator/superconductor interface. We consider the minimal model when these states appear because of the suppressed pairing constant within the interfacial normal layer. For thin normal layers we obtain a strongly peaked temperature dependence of the Gilbert damping coefficient which has been recently observed in such systems. For thicker normal layers the Gilbert damping monotonically increases down to the temperature…
The ends of manifolds with bounded geometry, linear growth and finite filling area
2002
We prove that simply connected open Riemannian manifolds of bounded geometry, linear growth and sublinear filling growth (e.g. finite filling area) are simply connected at infinity.
The handlebody group and the images of the second Johnson homomorphism
2020
Given an oriented surface bounding a handlebody, we study the subgroup of its mapping class group defined as the intersection of the handlebody group and the second term of the Johnson filtration: $\mathcal{A} \cap J_2$. We introduce two trace-like operators, inspired by Morita's trace, and show that their kernels coincide with the images by the second Johnson homomorphism $\tau_2$ of $J_2$ and $\mathcal{A} \cap J_2$, respectively. In particular, we answer by the negative to a question asked by Levine about an algebraic description of $\tau_2(\mathcal{A} \cap J_2)$. By the same techniques, and for a Heegaard surface in $S^3$, we also compute the image by $\tau_2$ of the intersection of the …
On the Dimension of Kakeya Sets in the First Heisenberg Group
2021
We define Kakeya sets in the Heisenberg group and show that the Heisenberg Hausdorff dimension of Kakeya sets in the first Heisenberg group is at least 3. This lower bound is sharp since, under our definition, the $\{xoy\}$-plane is a Kakeya set with Heisenberg Hausdorff dimension 3.
Direct imaging of current-induced antiferromagnetic switching revealing a pure thermomagnetoelastic switching mechanism in NiO
2021
We unambiguously identify the origin of the current-induced magnetic switching of insulating antiferromagnet/heavy metal bilayers. Previously, different reorientations of the Neel order for the same current direction were reported for different device geometries and different switching mechanisms were proposed. Here, we combine concurrent electrical readout and optical imaging of the switching of antiferromagnetic domains with simulations of the current-induced temperature and strain gradients. By comparing the switching in specially engineered NiO/Pt device and pulsing geometries, we can rule out spin-orbit torque based mechanisms and identify a thermomagnetoelastic mechanism to dominate t…
Magnetic Excitations in Tetrameric Clusters of Polyoxometalates Observed by Inelastic Neutron Scattering. Evidence for Anisotropic Exchange Interacti…
1997
Magnetic excitations in tetranuclear clusters of exchange-coupled metal ions encapsulated by polyoxotungstate ligands (1) have been observed by inelastic neutron scattering (INS) in the salts K10[M4(H2O)2(PW9O34)2]·nH2O, where M2+ = Mn, Co, and Ni. INS provides a much deeper and more detailed insight into the nature of the magnetic coupling in these clusters than bulk techniques. In particular, anisotropic exchange interactions are evidenced in the ferromagnetic Co4 cluster.
Substitution Effects in Double Perovskites: How the Crystal Structure Influences the Electronic Properties
2013
We systematically studied substituted Sr2FeReO6 with respect to experimental characterization and theoretical band structure calculations. In the framework of the tight-binding approach, hole- or electron-doping of Sr2MM’O6 were performed at the M or M’ positions either by transition or main group metals. Hole-doping, rather than electron-doping, has a favorable effect to improve the half-metallicity (Curie temperature and saturation magnetization) of the parent compound. When M is substituted by another metal, the original M’ metal will serve as a redox buffer (and vice versa). Substituting M by another metal with a size similar to that of the metal at M’ position causes disorder, which ha…
Concurrent magneto-optical imaging and magneto-transport readout of electrical switching of insulating antiferromagnetic thin films
2020
We demonstrate stable and reversible current induced switching of large-area ($> 100\;��m^2$) antiferromagnetic domains in NiO/Pt by performing concurrent transport and magneto-optical imaging measurements in an adapted Kerr microscope. By correlating the magnetic images of the antiferromagnetic domain changes and magneto-transport signal response in these current-induced switching experiments, we disentangle magnetic and non-magnetic contributions to the transport signal. Our table-top approach establishes a robust procedure to subtract the non-magnetic contributions in the transport signal and extract the spin-Hall magnetoresistance response associated with the switching of the antifer…
Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation
2013
Hyperpolarization has found many applications in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, its usage is still limited to the observation of relatively fast processes because of its short lifetimes. This issue can be circumvented by storing the hyperpolarization in a slowly relaxing singlet state. Symmetrical molecules hyperpolarized by Parahydrogen Induced Hyperpolarization (PHIP) provide a straightforward access to hyperpolarized singlet states because the initial parahydrogen singlet state is preserved at almost any magnetic field strength. In these systems, which show a remarkably long 1H singlet state lifetime of several minutes, the conversion of t…