Elucidating the Limit of Li Insertion into the Spinel Li4Ti5O12

In this work, we show that the well-known lithium-ion anode material, Li4Ti5O12, exhibits exceptionally high initial capacity of 310 mAh g-1 when it is discharged to 0.01 V. It maintains a reversible capacity of 230 mAh g-1, far exceeding the "theoretical" capacity of 175 mAh g-1 when this anode is lithiated to the composition Li7Ti5O12. Neutron diffraction analyses identify that additional Li reversibly enters into the Li7Ti5O12 to form Li8Ti5O12. density functional theory (DFT) calculations reveal the average potentials of the Li4Ti5O12 to Li7Ti5O12 step and the Li7Ti5O12 to Li8Ti5O12 step are 1.57 and 0.19 V, respectively, which are in excellent agreement with experimental results. Transmission electron microscopy (TEM) studies confirm that the irreversible capacity of Li4Ti5O12 during its first cycle originates from the formation of a solid electrolyte interface (SEI) layer. This work clarifies the fundamental lithiation mechanism of the Li4Ti5O12, when lithiated to 0.01 V vs Li

Developing high-impedance superconducting resonators and on-chip filters for semiconductor quantum dot circuit quantum electrodynamics

Spin-photon coupling presents an enticing opportunity for the long-range coupling of spin qubits. The spin-photon coupling rate $g_{s}$ is proportional to the charge-photon coupling rate $g_{c}$. To move deeper into the strong coupling regime, $g_{c}$ can be enhanced by fabricating high-impedance cavities using high kinetic inductance films. Here we report dc transport and microwave response investigations of niobium nitride (NbN) films of different thicknesses. The kinetic inductance increases rapidly as the film thickness is reduced below 50 nm and for 15 nm NbN films we measure a sheet kinetic inductance $L_{k,S}$ = 41.2 pH/$\Box$. As an application of the high kinetic inductance films, we fabricate compact LC filters that are commonly used to reduce microwave leakage in circuit quantum electrodynamics (cQED) devices. These filters feature up to 60 dB of attenuation near typical cavity resonance frequencies $f_c$ = 8 GHz

Fermi Surface reconstruction in the CDW state of CeTe3 observed by photoemission

CeTe3 is a layered compound where an incommensurate Charge Density Wave (CDW) opens a large gap (400 meV) in optimally nested regions of the Fermi Surface (FS), whereas other sections with poorer nesting remain ungapped. Through Angle-Resolved Photoemission, we identify bands backfolded according to the CDW periodicity. They define FS pockets formed by the intersection of the original FS and its CDW replica. Such pockets illustrate very directly the role of nesting in the CDW formation but they could not be detected so far in a CDW system. We address the reasons for the weak intensity of the folded bands, by comparing different foldings coexisting in CeTe3

Amplification of evanescent waves in a lossy left-handed material slab

We carry out finite-difference time-domain (FDTD) simulations, with a specially-designed boundary condition, on pure evanescent waves interacting with a lossy left-handed material (LHM) slab. Our results provide the first full-wave numerical evidence for the amplification of evanescent waves inside a LHM slab of finite absorption. The amplification is due to the interactions between the evanescent waves and the coupled surface polaritons at the two surfaces of the LHM slab and the physical process can be described by a simple model.Comment: 4 pages, 2 figure

Vanishing Hall Constant in the Stripe Phase of Cuprates

The Hall constant R_H is considered for the stripe structures. In order to explain the vanishing of R_H in LNSCO at x = 1/8, we use the relation of R_H to the Drude weight D as well as direct numerical calculation, to obtain results within the t-J model, where the stripes are imposed via a charge potential and a staggered magnetic field. The origin of R_H ~ 0 is related to a maximum in D and the minimal kinetic energy in stripes with a hole filling ~ 1/2. The same argument indicates on a possibility of R_H ~ 0 in the whole range of static stripes for x < 1/8.Comment: RevTeX, 4 pages, 5 figure

NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology

We have measured the effect of uniaxial stress on the threshold field ET for the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1 - e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This ecpression remains valid over more than two decades of ET, up to the highest fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity concentraction. The CDW transition temperature Tp decreases linearly with e at a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov de-Haas measurements show that the extremal area of the Fermi surface decreases with increasing strain. The results suggest that there is an intimate relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure

Anomalous asymmetry of magnetoresistance in NbSe3_3 single crystals

A pronounced asymmetry of magnetoresistance with respect to the magnetic field direction is observed for NbSe$_3$ crystals placed in a magnetic field perpendicular to their conducting planes. It is shown that the effect persists in a wide temperature range and manifests itself starting from a certain magnetic induction value $B_0$, which at $T=4.2$ K corresponds to the transition to the quantum limit, i.to the state where the Landay level splitting exceeds the temperature.Comment: 4 pages, 6 figures, to be appeared in JETP Let

Quantum Orders and Symmetric Spin Liquids

A concept -- quantum order -- is introduced to describe a new kind of orders that generally appear in quantum states at zero temperature. Quantum orders that characterize universality classes of quantum states (described by {\em complex} ground state wave-functions) is much richer then classical orders that characterize universality classes of finite temperature classical states (described by {\em positive} probability distribution functions). The Landau's theory for orders and phase transitions does not apply to quantum orders since they cannot be described by broken symmetries and the associated order parameters. We find projective representations of symmetry groups (which will be called projective symmetry groups) can be used to characterize quantum orders. With the help of quantum orders and the projective symmetry groups, we construct hundreds of symmetric spin liquids, which have SU(2), U(1) or $Z_2$ gauge structures at low energies. Remarkably, some of the stable quantum phases support gapless excitations even without any spontaneous symmetry breaking. We propose that it is the quantum orders (instead of symmetries) that protect the gapless excitations and make algebraic spin liquids and Fermi spin liquids stable. Since high $T_c$ superconductors are likely to be described by a gapless spin liquid, the quantum orders and their projective symmetry group descriptions lay the foundation for spin liquid approach to high $T_c$ superconductors.Comment: 58 pages, RevTeX4 home page: http://dao.mit.edu/~we