Electrons in correlated insulators are prevented from conducting by Coulomb repulsion between them. When an insulator-to-metal transition is induced in a correlated insulator by doping or heating, ...the resulting conducting state can be radically different from that characterized by free electrons in conventional metals. We report on the electronic properties of a prototypical correlated insulator vanadium dioxide in which the metallic state can be induced by increasing temperature. Scanning near-field infrared microscopy allows us to directly image nanoscale metallic puddles that appear at the onset of the insulator-to-metal transition. In combination with far-field infrared spectroscopy, the data reveal the Mott transition with divergent quasi-particle mass in the metallic puddles. The experimental approach used sets the stage for investigations of charge dynamics on the nanoscale in other inhomogeneous correlated electron systems.
Infrared band gap semiconductor nanocrystals are promising materials for exploring generation III photovoltaic concepts that rely on carrier multiplication or multiple exciton generation, the process ...in which a single high-energy photon generates more than one electron–hole pair. In this work, we present measurements of carrier multiplication yields and biexciton lifetimes for a large selection of PbS nanocrystals and compare these results to the well-studied PbSe nanocrystals. The similar bulk properties of PbS and PbSe make this an important comparison for discerning the pertinent properties that determine efficient carrier multiplication. We observe that PbS and PbSe have very similar biexciton lifetimes as a function of confinement energy. Together with the similar bulk properties, this suggests that the rates of multiexciton generation, which is the inverse of Auger recombination, are also similar. The carrier multiplication yields in PbS nanocrystals, however, are strikingly lower than those observed for PbSe nanocrystals. We suggest that this implies the rate of competing processes, such as phonon emission, is higher in PbS nanocrystals than in PbSe nanocrystals. Indeed, our estimations for phonon emission mediated by the polar Fröhlich-type interaction indicate that the corresponding energy-loss rate is approximately twice as large in PbS than in PbSe.
In correlated metals derived from Mott insulators, the motion of an electron is impeded by Coulomb repulsion due to other electrons. This phenomenon causes a substantial reduction in the electron's ...kinetic energy, leading to remarkable experimental manifestations in optical spectroscopy. The high-transition-temperature (Tc) superconducting cuprates are perhaps the most studied examples of such correlated metals. The occurrence of high-Tc superconductivity in the iron pnictides puts a spotlight on the relevance of correlation effects in these materials. Here, we present an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO. We find clear evidence of electronic correlations in metallic LaFePO with the kinetic energy of the electrons reduced to half of that predicted by band theory of nearly free electrons. We deduce that electronic many-body effects are important in the iron pnictides despite the absence of a Mott transition.
Summary Background Autologous haemopoietic stem-cell transplantation (HSCT) improves survival in patients with multiple myeloma, but disease progression remains an issue. Allogeneic HSCT might reduce ...disease progression, but can be associated with high treatment-related mortality. Thus, we aimed to assess effectiveness of allogeneic HSCT with non-myeloablative conditioning after autologous HSCT compared with tandem autologous HSCT. Methods In our phase 3 biological assignment trial, we enrolled patients with multiple myeloma attending 37 transplant centres in the USA. Patients (<70 years old) with adequate organ function who had completed at least three cycles of systemic antimyeloma therapy within the past 10 months were eligible for inclusion. We assigned patients to receive an autologous HSCT followed by an allogeneic HSCT (auto-allo group) or tandem autologous HSCTs (auto-auto group) on the basis of the availability of an HLA-matched sibling donor. Patients in the auto-auto group subsequently underwent a random allocation (1:1) to maintenance therapy (thalidomide plus dexamethasone) or observation. To avoid enrolment bias, we classified patients as standard risk or high risk on the basis of cytogenetics and β2-microglobulin concentrations. We used the Kaplan-Meier method to estimate differences in 3-year progression-free survival (PFS; primary endpoint) between patients with standard-risk disease in the auto-allo group and the best results from the auto-auto group (maintenance, observation, or pooled). This study is registered with ClinicalTrials.gov , number NCT00075829. Findings Between Dec 17, 2003, and March 30, 2007, we enrolled 710 patients, of whom 625 had standard-risk disease and received an autologous HSCT. 156 (83%) of 189 patients with standard-risk disease in the auto-allo group and 366 (84%) of 436 in the auto-auto group received a second transplant. 219 patients in the auto-auto group were randomly assigned to observation and 217 to receive maintenance treatment, of whom 168 (77%) completed this treatment. PFS and overall survival did not differ between maintenance and observation groups and pooled data were used. Kaplan-Meier estimates of 3-year PFS were 43% (95% CI 36–51) in the auto-allo group and 46% (42–51) in the auto-auto group (p=0·671); overall survival also did not differ at 3 years (77% 95% CI 72–84 vs 80% 77–84; p=0·191). Within 3 years, 87 (46%) of 189 patients in the auto-allo group had grade 3–5 adverse events as did 185 (42%) of 436 patients in the auto-auto group. The adverse events that differed most between groups were hyperbilirubinaemia (21 11% patients in the auto-allo group vs 14 3% in the auto-auto group) and peripheral neuropathy (11 6% in the auto-allo group vs 52 12% in the auto-auto group). Interpretation Non-myeloablative allogeneic HSCT after autologous HSCT is not more effective than tandem autologous HSCT for patients with standard-risk multiple myeloma. Further enhancement of the graft versus myeloma effect and reduction in transplant-related mortality are needed to improve the allogeneic HSCT approach. Funding US National Heart, Lung, and Blood Institute and the National Cancer Institute.
Single-cycle melphalan 200 mg/m
and autologous hematopoietic cell transplantation (AHCT) followed by lenalidomide (len) maintenance have improved progression-free survival (PFS) and overall survival ...(OS) for transplantation-eligible patients with multiple myeloma (MM). We designed a prospective, randomized, phase III study to test additional interventions to improve PFS by comparing AHCT, tandem AHCT (AHCT/AHCT), and AHCT and four subsequent cycles of len, bortezomib, and dexamethasone (RVD; AHCT + RVD), all followed by len until disease progression.
Patients with symptomatic MM within 12 months from starting therapy and without progression who were age 70 years or younger were randomly assigned to AHCT/AHCT + len (n = 247), AHCT + RVD + len (n = 254), or AHCT + len (n = 257). The primary end point was 38-month PFS.
The study population had a median age of 56 years (range, 20 to 70 years); 24% of patients had high-risk MM, 73% had a triple-drug regimen as initial therapy, and 18% were in complete response at enrollment. The 38-month PFS rate was 58.5% (95% CI, 51.7% to 64.6%) for AHCT/AHCT + len, 57.8% (95% CI, 51.4% to 63.7%) for AHCT + RVD + len, and 53.9% (95% CI, 47.4% to 60%) for AHCT + len. For AHCT/AHCT + len, AHCT + RVD + len, and AHCT + len, the OS rates were 81.8% (95% CI, 76.2% to 86.2%), 85.4% (95% CI, 80.4% to 89.3%), and 83.7% (95% CI, 78.4% to 87.8%), respectively, and the complete response rates at 1 year were 50.5% (n = 192), 58.4% (n = 209), and 47.1% (n = 208), respectively. Toxicity profiles and development of second primary malignancies were similar across treatment arms.
Second AHCT or RVD consolidation as post-AHCT interventions for the up-front treatment of transplantation-eligible patients with MM did not improve PFS or OS. Single AHCT and len should remain as the standard approach for this population.
Radiative heat transfer (RHT) has a central role in entropy generation and energy transfer at length scales ranging from nanometres to light years
. The blackbody limit
, as established in Max ...Planck's theory of RHT, provides a convenient metric for quantifying rates of RHT because it represents the maximum possible rate of RHT between macroscopic objects in the far field-that is, at separations greater than Wien's wavelength
. Recent experimental work has verified the feasibility of overcoming the blackbody limit in the near field
, but heat-transfer rates exceeding the blackbody limit have not previously been demonstrated in the far field. Here we use custom-fabricated calorimetric nanostructures with embedded thermometers to show that RHT between planar membranes with sub-wavelength dimensions can exceed the blackbody limit in the far field by more than two orders of magnitude. The heat-transfer rates that we observe are in good agreement with calculations based on fluctuational electrodynamics. These findings may be directly relevant to various fields, such as energy conversion, atmospheric sciences and astrophysics, in which RHT is important.
Abstract
Nanofibrils play a pivotal role in spider silk and are responsible for many of the impressive properties of this unique natural material. However, little is known about the internal ...structure of these protein fibrils. We carry out polarized Raman and polarized Fourier-transform infrared spectroscopies on native spider silk nanofibrils and determine the concentrations of six distinct protein secondary structures, including β-sheets, and two types of helical structures, for which we also determine orientation distributions. Our advancements in peak assignments are in full agreement with the published silk vibrational spectroscopy literature. We further corroborate our findings with X-ray diffraction and magic-angle spinning nuclear magnetic resonance experiments. Based on the latter and on polypeptide Raman spectra, we assess the role of key amino acids in different secondary structures. For the recluse spider we develop a highly detailed structural model, featuring seven levels of structural hierarchy. The approaches we develop are directly applicable to other proteinaceous materials.
The insulator‐to‐metal transition (IMT) in vanadium dioxide (VO2) can enable a variety of optics applications, including switching and modulation, optical limiting, and tuning of optical resonators. ...Despite the widespread interest in VO2 for optics, the wavelength‐dependent optical properties across its IMT are scattered throughout the literature, are sometimes contradictory, and are not available at all in some wavelength regions. Here, the complex refractive index of VO2 thin films across the IMT is characterized for free‐space wavelengths from 300 nm to 30 µm, using broadband spectroscopic ellipsometry, reflection spectroscopy, and the application of effective‐medium theory. VO2 films of different thicknesses are studied, on two different substrates (silicon and sapphire), and grown using different synthesis methods (sputtering and sol–gel). While there are differences in the optical properties of VO2 synthesized under different conditions, these differences are surprisingly small in the ≈2–11 µm range where the insulating phase of VO2 also has relatively low optical loss. It is anticipated that the refractive‐index datasets from this article will be broadly useful for modeling and design of VO2‐based optical and optoelectronic components, especially in the mid‐wave and long‐wave infrared.
The optical properties of vanadium dioxide (VO2) for wavelengths from 0.3 to 30 µm are described, as VO2 traverses its insulator‐to‐metal phase transition. A combination of characterization techniques and effective‐medium theory is used to explore films of different thicknesses, on different substrates, and grown using different methods, making the work broadly useful for modeling VO2‐based optical and optoelectronic components.
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