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Deconfined quantum criticality and conformal phase transition in two-dimensional antiferromagnets1
by Flavio S. Nogueira and Asle Sudbø.
Deconfined quantum criticality of two-dimensional SU(2) quantum antiferromagnets featuring a transition from an antiferromagnetically ordered ground state to a so-called valence-bond solid state, is governed by a non-compact CP1 model with a Maxwell term in 2+1 spacetime dimensions. We introduce a new perspective on deconfined quantum criticality within a field-theoretic framework based on an expansion in powers of ε=4-d for fixed number N of complex matter fields. We show that in the allegedly weak first-order transition regime, a so-called conformal phase transition leads to a genuine deconfined quantum critical point. In such a transition, the gap vanishes when the critical point is approached from above and diverges when it is approached from below. We also find that the spin stiffness has a universal jump at the critical point.
A family of low-energy low-density silicon allotropes built from the diamond structure2
by L. Pizzagalli.
First-principles calculations have been performed to investigate structural and energetics properties of a family of silicon allotropes, built from the cubic diamond structure. These phase are characterized by a lower density compared to silicon diamond, and low relative energies ranging from 0.067 eV/at. to 0.089 eV/at. only. One of its member, the L1β phase, is shown to become more stable than the diamond structure for hydrostatic tensile pressure of 7.5 GPa. Its low density and the presence of 8-fold rings in the structure also suggest that it might have potential use as a lithium container.
Low-temperature dipolar echoes in amorphous dielectrics: Significance of relaxation and decoherence free two-level systems3
by A. L. Burin et al.
The theoretical model for dielectric echoes in amorphous solids at low temperatures has been developed and applied to the recent two- and three-pulse echo experimental data in borosilicate glass BK7 where the amplitude of dipolar echoes has been observed for unprecedentedly long delay times extending the experimental window for studying the decay by several orders of magnitude. We show that at long delay times the echo amplitude is determined by a small subset of two-level systems (TLSs) with negligible relaxation and decoherence because of their weak coupling to phonons. The universal statistics of coupling is obtained by assuming that different TLS elastic tensor components are almost independent. Under this assumption the echo decay can be described approximately by the power law time dependences with different powers at times shorter and longer than the typical TLS relaxation time. These predictions are in a very good agreement with the experimental data and can be used to extract TLS relaxation and decoherence rates from the echo experiments.
Oriented gap opening in the magnetically ordered state of iron pnictides: An impact of intrinsic unit cell doubling on the Fe square lattice by As atoms4
by Ningning Hao et al.
We show that the complicated band reconstruction near Fermi surfaces in the magnetically ordered state of iron pnictides observed by angle-resolved photoemission spectroscopies (ARPES) can be understood in a mean-field level if the intrinsic unit cell doubling due to As atoms is properly considered as shown in the recently constructed S4 microscopic effective model. The (0,π) or (π,0) collinear antiferromagnetic (C-AFM) order does not open gaps between two points at Fermi surfaces linked by the ordered wave vector but forces a band reconstruction involving four points in the unfolded Brillouin zone (BZ) and gives rise to small pockets or hot spots. The S4 symmetry naturally chooses a staggered orbital order over a ferro-orbital order to coexist with the C-AFM order. These results strongly suggest that the kinematics based on the S4 symmetry captures the essential low-energy physics of iron-based superconductors.
Multifractal analysis of dynamic infrared imaging of breast cancer5
by E. Gerasimova et al.
The wavelet transform modulus maxima (WTMM) method was used in a multifractal analysis of skin breast temperature time-series recorded using dynamic infrared (IR) thermography. Multifractal scaling was found for healthy breasts as the signature of a continuous change in the shape of the probability density function (pdf) of temperature fluctuations across time scales from ∼0.3 to 3 s. In contrast, temperature time-series from breasts with malignant tumors showed homogeneous monofractal temperature fluctuations statistics. These results highlight dynamic IR imaging as a very valuable non-invasive technique for preliminary screening in asymptomatic women to identify those with risk of breast cancer.
- Flavio S. Nogueira and Asle Sudbø. 2013. Deconfined quantum criticality and conformal phase transition in two-dimensional antiferromagnets. EPL, 104, 56004. DOI: 10.1209/0295-5075/104/56004 [↩]
- L. Pizzagalli. 2013. A family of low-energy low-density silicon allotropes built from the diamond structure. EPL, 104, 56005. DOI: 10.1209/0295-5075/104/56005 [↩]
- A. L. Burin et al. 2013. Low-temperature dipolar echoes in amorphous dielectrics: Significance of relaxation and decoherence free two-level systems. EPL, 104, 57006. DOI: 10.1209/0295-5075/104/57006 [↩]
- Ningning Hao et al. 2013. Oriented gap opening in the magnetically ordered state of iron pnictides: An impact of intrinsic unit cell doubling on the Fe square lattice by As atoms. EPL, 104, 57007. DOI: 10.1209/0295-5075/104/57007 [↩]
- E. Gerasimova et al. 2013. Multifractal analysis of dynamic infrared imaging of breast cancer. EPL, 104, 68001. DOI: 10.1209/0295-5075/104/68001 [↩]
