The crossover from weak to strong correlations in parabolic quantum dots at zero magnetic field is studied by numerically exact path-integral Monte Carlo simulations for up to eight electrons. By the use of a multilevel blocking algorithm, the simulations are carried out free of the fermion sign problem. We obtain a universal crossover governed only by the density parameter r s . For r s . r c , the data are consistent with a Wigner molecule description, while, for r s , r c , Fermi liquid behavior is recovered. The crossover value r c ഠ 4 is surprisingly small. [S0031-9007 (99)08929-2] PACS numbers: 73.20.Dx, 71.10.Ay, 71.10.CaQuantum dots can be considered as solid-state artificial atoms with tunable properties. Confining a small number of electrons N in a two-dimensional electron gas in semiconductor heterostructures, a number of interesting effects arising from the interplay between confinement and the Coulomb interaction between the electrons can be observed [1,2]. Since the confinement potential is usually quite shallow, the long-ranged Coulomb interaction among the electrons plays a prominent role, and in contrast to conventional atoms effective single-particle approximations quickly become unreliable. In the low-density (stronginteraction) limit, r s !`, classical considerations suggest a Wigner crystal-like phase with electrons spatially arranged in shells [3]. With quantum fluctuations, such a phase is best described as a Wigner molecule. In contrast, for high densities (weak interactions), r s ! 0, a Fermi liquidlike description is expected to be valid, where it is more appropriate to think of the behavior as resulting from the single-particle orbitals being filled. The noninteracting limit [4] is then typically used as a starting point for the theoretical description of quantum dots.To date, no reliable information exists for the crossover between these two limits. This is mainly due to a complete lack of sufficiently accurate methods that are able to cover the full range of r s , especially when no magnetic field is present. Exact diagonalization techniques are limited to very small particle numbers and small r s ; otherwise, a large error due to the truncation of the Hilbert space arises [5]. Hartree-Fock calculations become increasingly unreliable for large r s and are known to incorrectly favor spin-polarized states [6]. Similarly, density functional calculations [7] introduce uncontrolled approximations in the absence of exact reference data. In principle, the quantum Monte Carlo (QMC) method is the best candidate for producing reliable data for quantum dots. Unfortunately, the notorious fermion sign problem makes direct QMC simulations almost impossible [8]. To avoid the sign problem, the fixed-node approximation and a related variational approach have been employed in Ref. [9], but the results are no longer exact.In this Letter, we adopt a radically different approach to fermion QMC simulations, based on the recently developed multilevel blocking (MLB) algorithm [10,11]. The MLB algorithm is ab...
The dynamics of spin-boson systems at very low temperatures has been studied
using a real-time path-integral simulation technique which combines a
stochastic Monte Carlo sampling over the quantum fluctuations with an exact
treatment of the quasiclassical degrees of freedoms. To a large degree, this
special technique circumvents the dynamical sign problem and allows the
dynamics to be studied directly up to long real times in a numerically exact
manner. This method has been applied to two important problems: (1) crossover
from nonadiabatic to adiabatic behavior in electron transfer reactions, (2) the
zero-temperature dynamics in the antiferromagnetic Kondo region 1/2
The standard treatment for high-grade serous ovarian cancer is primary debulking surgery followed by chemotherapy. The extent of metastasis and invasive potential of lesions can influence the outcome of these primary surgeries. Here, we explored the underlying mechanisms that could increase metastatic potential in ovarian cancer. We discovered that FABP4 (fatty acid binding protein) can substantially increase the metastatic potential of cancer cells. We also found that miR-409-3p regulates FABP4 in ovarian cancer cells and that hypoxia decreases miR-409-3p levels. Treatment with DOPC nanoliposomes containing either miR-409-3p mimic or FABP4 siRNA inhibited tumor progression in mouse models. With RPPA and metabolite arrays, we found that FABP4 regulates pathways associated with metastasis and affects metabolic pathways in ovarian cancer cells. Collectively, these findings demonstrate that FABP4 is functionally responsible for aggressive patterns of disease that likely contribute to poor prognosis in ovarian cancer.
Large-scale computer simulations with more than four million particles have been performed to study the melting transition in a two-dimensional hard disk fluid. The van der Waals loop previously observed in the pressure-density relationship of smaller simulations is shown to disappear systematically with increase in sample size, but even with these large system sizes, the freezing transition still exhibits what appears to be weakly first-order behavior, though the scaling of the bond orientation order is consistent with the Halperin-Nelson-Young picture. Above this freezing transition region, scaling analysis of the translational order yields a lower bound for the melting density that is much higher than previously thought and provides compelling evidence that the solid phase first melts into a hexatic phase via a continuous transition, before it goes into the isotropic phase.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.