Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field

We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. Application of a magnetic field perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular interactions turn this equilibrium state into a ferromagnetically ordered phase. However, long range ferromagnetic correlations nearly disappear for fields larger 5.5 T, possibly suggesting the existence of a quantum critical point.Comment: 4 pages, 4 figure

In Their Own Words: Asian Immigrants Experiences Navigating Language Barriers in the United States

New immigrant arrivals to the United States face many challenges and obstacles when navigating their daily lives. For Asian immigrants, these include language and cultural obstacles that impact those who arrive with little to no proficiency in English. But navigating life in America also impacts English-speaking immigrants as they adjust to life in a new country with its own unique linguistic and cultural quirks.In 2021, Pew Research Center conducted 49 focus groups with Asian immigrants to understand the challenges they faced, if any, after arriving in the country. The focus groups consisted of 18 distinct Asian origins and were conducted in 17 Asian languages.This report explores three broad themes from the focus group discussions: the challenges Asian immigrants have faced in navigating daily life and communicating in English; tools and strategies they used to learn the language; and types of help they received from others in adapting to English-speaking settings. The experiences discussed may not resonate with all Asian U.S. immigrants, but the study sought to capture a wide range of views by including participants of different languages, immigration or refugee experiences, educational backgrounds and income levels

Diverse Cultures and Shared Experiences Shape Asian American Identities

Pew Research Center conducted this analysis to understand the rich diversity of people of Asian origin or ancestry living in the United States and their views of identity. The study is part of the Center's multiyear, comprehensive, in-depth quantitative and qualitative research effort focused on the nation's Asian population. Its centerpiece is this nationally representative survey of 7,006 Asian adults exploring the experiences, attitudes and views of Asians living in the U.S. The survey sampled U.S. adults who self-identify as Asian, either alone or in combination with other races or Hispanic ethnicity. It was offered in six languages: Chinese (Simplified and Traditional), English, Hindi, Korean, Tagalog and Vietnamese. Responses were collected from July 5, 2022, to Jan. 27, 2023, by Westat on behalf of Pew Research Center

Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities

Localized magnetic moments have been predicted to develop in graphene samples with vacancies or adsorbates. The interplay between such magnetic impurities and graphene's Dirac quasiparticles leads to remarkable many-body phenomena, which have so far proved elusive to experimental efforts. In this article, we study the thermodynamic, spectral and transport signatures of quantum criticality and Kondo physics of a dilute ensemble of atomic impurities in graphene. We consider vacancies and adatoms that either break or preserve graphene's $C_{3v}$ and inversion symmetries. In a neutral graphene sample, all cases display symmetry-dependent quantum criticality, leading to enhanced impurity scattering for asymmetric impurities, in a manner analogous to bound-state formation by nonmagnetic resonant scatterers. Kondo correlations emerge only in the presence of a back gate, with estimated Kondo temperatures well within the experimentally accessible domain for all impurity types. For symmetry-breaking impurities at charge neutrality, quantum criticality is signaled by $T^{-2}$ resistivity scaling, leading to full insulating behavior at low temperatures, while low-temperature resistivity plateaus appear both in the non-critical and Kondo regimes. By contrast, the resitivity contribution from symmetric vacancies and hollow-site adsorbates vanishes at charge neutrality and for arbitrary back gate voltages, respectively. This implies that local probing methods are required for the detection of both Kondo and quantum critical signatures in these symmetry-preserving cases.Comment: Final published version, with corrected figures, improved notation, and added references. 12 pages, including 8 figures and one appendi

Alignment Of Magnetic Anisotropy Axes In Crystals Of Mn12 Acetate And Mn12-tBuAc Molecular Nanomagnets: Angle-Dependent Ac Susceptibility Study

We report the results of angular-dependent ac susceptibility experiments performed on two derivatives of Mn12 single-molecular magnets: the well-known Mn12 acetate, which contains disordered acetic acid molecules in interstitial sites of the crystal structure and Mn12-tBuAc, for which solvent molecules are very well ordered in the structure. Our results show (a) that the angular variation is very similar in the two compounds investigated and compatible with a maximum misalignment of the anisotropy axes of less than 3° and (b) that the tunneling rate is faster for the better ordered Mn12-tBuAc compound. These experiments question interstitial disorder as the dominant origin of the thermally activated tunneling phenomenon

Interaction effects on a Majorana zero mode leaking into a quantum dot

We have recently shown [Phys. Rev. B {\bf 89}, 165314 (2014)] that a non--interacting quantum dot coupled to a one--dimensional topological superconductor and to normal leads can sustain a Majorana mode even when the dot is expected to be empty, \emph{i.e.}, when the dot energy level is far above the Fermi level of he leads. This is due to the Majorana bound state of the wire leaking into the quantum dot. Here we extend this previous work by investigating the low--temperature quantum transport through an {\it interacting} quantum dot connected to source and drain leads and side--coupled to a topological wire. We explore the signatures of a Majorana zero--mode leaking into the quantum dot for a wide range of dot parameters, using a recursive Green's function approach. We then study the Kondo regime using numerical renormalization group calculations. We observe the interplay between the Majorana mode and the Kondo effect for different dot-wire coupling strengths, gate voltages and Zeeman fields. Our results show that a "0.5" conductance signature appears in the dot despite the interplay between the leaked Majorana mode and the Kondo effect. This robust feature persists for a wide range of dot parameters, even when the Kondo correlations are suppressed by Zeeman fields and/or gate voltages. The Kondo effect, on the other hand, is suppressed by both Zeeman fields and gate voltages. We show that the zero--bias conductance as a function of the magnetic field follows a well--known universality curve. This can be measured experimentally, and we propose that the universal conductance drop followed by a persistent conductance of $0.5\,e^2/h$ is evidence of the presence of Majorana--Kondo physics. These results confirm that this "0.5" Majorana signature in the dot remains even in the presence of the Kondo effect.Comment: 19 pages, 12 figure

Universal critical behavior of the two-dimensional Ising spin glass

We use finite size scaling to study Ising spin glasses in two spatial dimensions. The issue of universality is addressed by comparing discrete and continuous probability distributions for the quenched random couplings. The sophisticated temperature dependency of the scaling fields is identified as the major obstacle that has impeded a complete analysis. Once temperature is relinquished in favor of the correlation length as the basic variable, we obtain a reliable estimation of the anomalous dimension and of the thermal critical exponent. Universality among binary and Gaussian couplings is confirmed to a high numerical accuracy

Universal critical behavior of the two-dimensional Ising spin glass

We use finite size scaling to study Ising spin glasses in two spatial dimensions. The issue of universality is addressed by comparing discrete and continuous probability distributions for the quenched random couplings. The sophisticated temperature dependency of the scaling fields is identified as the major obstacle that has impeded a complete analysis. Once temperature is relinquished in favor of the correlation length as the basic variable, we obtain a reliable estimation of the anomalous dimension and of the thermal critical exponent. Universality among binary and Gaussian couplings is confirmed to a high numerical accuracy