831 research outputs found

### Entry pathways of herpes simplex virus type 1 into human keratinocytes are dynamin- and cholesterol-dependent

Herpes simplex virus type 1 (HSV-1) can enter cells via endocytic pathways or direct fusion at the plasma membrane depending on the cell line and receptor(s). Most studies into virus entry have used cultured fibroblasts but since keratinocytes represent the primary entry site for HSV-1 infection in its human host, we initiated studies to characterize the entry pathway of HSV-1 into human keratinocytes. Electron microscopy studies visualized free capsids in the cytoplasm and enveloped virus particles in vesicles suggesting viral uptake both by direct fusion at the plasma membrane and by endocytic vesicles. The ratio of the two entry modes differed in primary human keratinocytes and in the keratinocyte cell line HaCaT. Inhibitor studies further support a role for endocytosis during HSV-1 entry. Infection was inhibited by the cholesterol-sequestering drug methyl-beta-cyclodextrin, which demonstrates the requirement for host cholesterol during virus entry. Since the dynamin-specific inhibitor dynasore and overexpression of a dominant-negative dynamin mutant blocked infection, we conclude that the entry pathways into keratinocytes are dynamin-mediated. Electron microscopy studies confirmed that virus uptake is completely blocked when the GTPase activity of dynamin is inhibited. Ex vivo infection of murine epidermis that was treated with dynasore further supports the essential role of dynamin during entry into the epithelium. Thus, we conclude that HSV-1 can enter human keratinocytes by alternative entry pathways that require dynamin and host cholesterol

### Quantum replica approach to the under-screened Kondo model

We extend the Schwinger boson large N treatment of the underscreened Kondo
model in a way that correctly captures the finite elastic phase shift in the
singular Fermi liquid. The new feature of the approach, is the introduction of
a flavor quantum number with K possible values, associated with the Schwinger
boson representation. The large N limit is taken maintaining the ratio k=K/N
fixed. This approach differs from previous approaches, in that we do not
explicitly enforce a constraint on the spin representation of the Schwinger
bosons. Instead, the energetics of the Kondo model cause the bosonic degrees of
freedom to ``self assemble'' into a ground-state in which the spins of K bosons
and N-K conduction electrons are antisymmetrically arranged into a Kondo
singlet. With this device, the large N limit can be taken, in such a way that a
fraction K/N of the Abrikosov Suhl resonance is immersed inside the Fermi sea.
We show how this method can be used to model the full energy dependence of the
singular Abrikosov Suhl resonance in the underscreened Kondo model and the
field-dependent magnetization.Comment: Revised draft, with plots explicitly showing logarithmic scaling of
inverse coupling constant. Small corrections prior to submission to journa

### Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature

The thermal conductivity of YbRh2Si2 has been measured down to very low
temperatures under field in the basal plane. An additional channel for heat
transport appears below 30 mK, both in the antiferromagnetic and paramagnetic
states, respectively below and above the critical field suppressing the
magnetic order. This excludes antiferromagnetic magnons as the origin of this
additional contribution to thermal conductivity. Moreover, this low temperature
contribution prevails a definite conclusion on the validity or violation of the
Wiedemann-Franz law at the field-induced quantum critical point. At high
temperature in the paramagnetic state, the thermal conductivity is sensitive to
ferromagnetic fluctuations, previously observed by NMR or neutron scattering
and required for the occurrence of the sharp electronic spin resonance
fracture.Comment: 11 pages + Supplementary Material

### Non Fermi Liquid behavior in the under-screened Kondo model

Using the Schwinger boson spin representation, we reveal a new aspect to the
physics of a partially screened magnetic moment in a metal, as described by the
spin $S$ Kondo model. We show that the residual ferromagnetic interaction
between a partially screened spin and the electron sea destabilizes the Landau
Fermi liquid, forming a singular Fermi liquid with a $1/ (T \ln ^{4}
(T_{K}/T))$ divergence in the low temperature specific heat coefficient
$C_{V}/T$. A magnetic field $B$ tunes this system back into Landau Fermi liquid
with a Fermi temperature proportional to $B \ln^2 (T_K/B)$. We discuss a
possible link with field-tuned quantum criticality in heavy electron materials.Comment: References corrected. Minor changes to tex

### Bose-Einstein condensation and entanglement in magnetic systems

We present a study of magnetic field induced quantum phase transitions in
insulating systems. A generalized scaling theory is used to obtain the
temperature dependence of several physical quantities along the quantum
critical trajectory ($H=H_{C}$, $T\to0$) where $H$ is a longitudinal external
magnetic field and $H_{C}$ the critical value at which the transition occurs.
We consider transitions from a spin liquid at a critical field $H_{C1}$ and
from a fully polarized paramagnet, at $H_{C2}$, into phases with long range
order in the transverse components. The transitions at $H_{C1}$ and $H_{C2}$
can be viewed as Bose-Einstein condensations of magnons which however belong to
different universality classes since they have different values of the dynamic
critical exponent $z$. Finally, we use that the magnetic susceptibility is an
entanglement witness to discuss how this type of correlation sets in as the
system approaches the quantum critical point along the critical trajectory,
$H=H_{C2}$, $T\to0$.Comment: 7 pages, 1 Table; accepted version; changes in text and new
reference

### Thermoelectric response near a quantum critical point of beta-YbAlB4 and YbRh2Si2: A comparative study

The thermoelectric coefficients have been measured on the Yb-based heavy
fermion compounds beta-YbAlB4 and YbRh2Si2 down to a very low temperature. We
observe a striking difference in the behavior of the Seebeck coefficient, S in
the vicinity of the Quantum Critical Point (QCP) in the two systems. As the
critical field is approached, S/T enhances in beta-YbAlB4 but is drastically
reduced in YbRh2Si2. While in the former system, the ratio of
thermopower-to-specific heat remains constant, it drastically drops near the
QCP in YbRh2Si2. In both systems, on the other hand, the Nernst coefficient
shows a diverging behavior near the QCP. The results provide a new window to
the way various energy scales of the system behave and eventually vanish near a
QCP

### Antiferromagnetism and Superconductivity in CeRhIn$_5$

We discuss recent results on the heavy fermion superconductor CeRhIn$_5$
which presents ideal conditions to study the strong coupling between the
suppression of antiferromagnetic order and the appearance of unconventional
superconductivity. The appearance of superconductivity as function of pressure
is strongly connected to the suppression of the magnetic order. Under magnetic
field, the re-entrance of magnetic order inside the superconducting state shows
that antiferromagnetism nucleates in the vortex cores. The suppression of
antiferromagnetism in CeRhIn$_5$ by Sn doping is compared to that under
hydrostatic pressure.Comment: 6 pages, 8 figures, to be published in Proc. Int. Conf. Heavy
Electrons (ICHE2010) J. Phys. Soc. Jpn. 80 (2011

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