T. J. Williams

Imaging the Fano lattice to ‘hidden order’ transition in URu2Si2

Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called ‘heavy fermions’. In URu2Si2 these effects begin at temperatures around 55 K but they are suddenly altered by an unidentified electronic phase transition at To = 17.5 K. Whether this is conventional ordering of the k-space states, or a change in the hybridization of the r-space states at each U atom, is unknown. Here we use spectroscopic imaging scanning tunnelling microscopy (SI-STM) to image the evolution of URu2Si2 electronic structure simultaneously in r-space and k-space. Above To, the ‘Fano lattice’ electronic structure predicted for Kondo screening of a magnetic lattice is revealed. Below To, a partial energy gap without any associated density-wave signatures emerges from this Fano lattice. Heavy-quasiparticle interference imaging within this gap reveals its cause as the rapid splitting below To of a light k-space band into two new heavy fermion bands. Thus, the URu2Si2 ‘hidden order’ state emerges directly from the Fano lattice electronic structure and exhibits characteristics, not of a conventional density wave, but of sudden alterations in both the hybridization at each U atom and the associated heavy fermion states.

Patients with lung cancer and paraneoplastic Hu syndrome harbor HuD-specific type 2 CD8+ T cells

Paraneoplastic neurologic disorders (PNDs) offer an uncommon opportunity to study human tumor immunity and autoimmunity. In small cell lung cancer (SCLC), expression of the HuD neuronal antigen is thought to lead to immune recognition, suppression of tumor growth, and, in a subset of patients, triggering of the Hu paraneoplastic neurologic syndrome. Antigen-specific CTLs believed to contribute to disease pathophysiology were described 10 years ago in paraneoplastic cerebellar degeneration. Despite parallel efforts, similar cells have not been defined in Hu patients. Here, we have identified HuD-specific T cells in Hu patients and provided an explanation for why their detection has been elusive. Different Hu patients harbored 1 of 2 kinds of HuD-specific CD8+ T cells: classical IFN-gamma-producing CTLs or unusual T cells that produced type 2 cytokines, most prominently IL-13 and IL-5, and lacked cytolytic activity. Further, we found evidence that SCLC tumor cells produced type 2 cytokines and that these cytokines trigger naive CD8+ T cells to adopt the atypical type 2 phenotype. These observations demonstrate the presence of an unusual noncytotoxic CD8+ T cell in patients with the Hu paraneoplastic syndrome and suggest that SCLC may evade tumor immune surveillance by skewing tumor antigen-specific T cells to this unusual noncytolytic phenotype.

Li(Zn,Mn)As as a new generation ferromagnet based on a I–II–V semiconductor

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li(1+y)(Zn(1-x)Mn(x))As in bulk materials. Ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess (y=0.05-0.2) compounds with Mn concentrations of x=0.02-0.15, which have p-type metallic carriers. This is presumably due to excess Li in substitutional Zn sites. Semiconducting LiZnAs, ferromagnetic Li(Zn,Mn)As, antiferromagnetic LiMnAs, and superconducting LiFeAs systems share square lattice As layers, which may enable development of novel junction devices in the future.

Absence of superconductivity in single-phase CaFe2As2 under hydrostatic pressure

Recent high-pressure studies found that structural/magnetic phase transitions are very pressure sensitive in

Superconducting state coexisting with a phase-separated static magnetic order in (Ba,K)Fe2As2, (Sr,Na)Fe2As2, and CaFe2As2

{\text{CaFe}}_{2}{\text{As}}_{2}

Muon-spin-relaxation studies of magnetic order and superfluid density in antiferromagnetic NdFeAsO, BaFe2As2, and superconducting Ba1-xKxFe2As2

and that superconductivity can be achieved under modest pressure, although details of the sharpness and temperature of transitions vary between liquid medium and gas medium measurements. To better understand this issue, we performed high-pressure susceptibility and transport studies on

A T cell receptor associated with naturally occurring human tumor immunity

{\text{CaFe}}_{2}{\text{As}}_{2}

Spin ice: magnetic excitations without monopole signatures using muon spin rotation.

, using helium as the pressure medium. The signatures of the transitions to the low-temperature orthorhombic and collapsed tetragonal phases remained exceptionally sharp, and no signature of bulk superconductivity was found under our hydrostatic conditions. Our results suggest that superconductivity in

(La1-xBax)(Zn1-xMnx)AsO: A two-dimensional 1111-type diluted magnetic semiconductor in bulk form

{\text{CaFe}}_{2}{\text{As}}_{2}

Muon spin rotation measurement of the magnetic field penetration depth in Ba ( Fe 0.926 Co 0.074 ) 2 As 2 : Evidence for multiple superconducting gaps

is associated with a low-temperature, multicrystallographic-phase sample that is the result of nonhydrostatic conditions associated with the combination of a first-order structural phase transition and frozen liquid media.