High-harmonic spectroscopy of quantum phase transitions in a high-Tc superconductor

We report on the nonlinear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO, observed through high harmonic generation. While the linear optical response of the material is largely unchanged when cooling across the phase transitions, the nonlinear optical response sensitively imprints two critical points, one at the critical temperature of the cuprate with the exponential growth of the surface harmonic yield in the superconducting phase and another critical point, which marks the transition from strange metal to pseudogap phase. To reveal the underlying microscopic quantum dynamics, a strong-field quasi-Hubbard model was developed, which describes the measured optical response dependent on the formation of Cooper pairs. Further, the theory provides insight into the carrier scattering dynamics and allows us to differentiate between the superconducting, pseudogap, and strange metal phases. The direct connection between nonlinear optical response and microscopic dynamics provides a powerful methodology to study quantum phase transitions in correlated materials. Further implications are light wave control over intricate quantum phases, light–matter hybrids, and application for optical quantum computing.

Attosecond technology (1), specifically the process of high harmonic generation (HHG) (2–4), provides an all-optical probe of the microscopic dynamics of atoms, molecules, and solids. Shortly after the first observation of high harmonics in atoms, their generation was understood (4–6) as arising from electron recollision after strong field photoionization and excursion in the continuum. Since the harmonic signal strongly depends on the electron recollision angle and time, high-harmonic spectroscopy (HHS) is a sensitive nonlinear probe of microscopic electronic structure with atomic spatial and suboptical cycle temporal resolution. HHS of solids (7, 8), two-dimensional materials (9, 10), or nanostructured media (11, 12) differs from the gas phase since the optical field–driven electronic wave packet is delocalized over many lattice sites, the wave function depends on the lattice momentum, and a hole has to match the electron’s momentum for recombination to occur (13, 14). Recent experimental efforts extended HHS as nonperturbative probe to quantum materials (9, 10, 15, 16) and to topological insulators (17–19). There have also been several theoretical advances, which suggest using strong fields to probe the physics of Mott insulators (20, 21), alongside the possibility of optically modifying strongly correlated matter (22) and tracking optically induced phase transitions (23), with a recent experiment reported in ref. 24.The sensitivity of HHS to the intricate microscopic details of carriers and lattice predestines HHS to investigate strong interactions and quantum correlations which lead to fascinating new states of matter such as superconductivity. The phase transition into a strongly correlated superconductive state is described by the spontaneous symmetry breaking of the U(1) redundancy when cooling below the critical temperature Tc of the material. As we will show, HHS is a sensitive probe of the dynamic evolution of the superconducting phase transition since the formation of composite bosons by pairing two fermionic spin-1/2 particles (Cooper pairs) changes the distribution of charge carriers, and this sensitively registers in the high harmonic amplitudes and spectral distribution. Pictorially, this is described in SI Appendix, Fig. S1, by a three-step model, consisting of 1) interband excitation process, 2) intraband acceleration, and 3) interband recombination. Pairing below T_c splits the bands by opening a superconducting gap Δ, and in the strongly correlated phase, the three processes of harmonic generation occur within the effective band structure for the Cooper pairs. We will also show that HHS can identify additional phase transitions between quantum phases in the strongly correlated material which are not accessible through the linear optical response, and they are difficult to detect with established methods such as superconducting quantum interference device (SQUID) magnetometry or four-probe transport measurements.A conventional superconductor can be described by the Anderson–Higgs mechanism, which explains that an optical nonlinear response is due to a gapless phase mode (Nambu–Goldstein) and a gapped amplitude mode (Higgs) of the ordering parameter. In the simplest case, and depending on the strength and type of excitation, Boltzmann and Ginzburg–Landau theories (25, 26) predict a second-order response, which mixes with the excitation mode (27, 28), thus the generation of the third harmonic (29). Unconventional high-Tc superconductors are of tremendous interest for a wide range of applications ranging from electronic devices and information processing devices to optical quantum computers and quantum simulators. However, due to their rich landscape of quantum phases and the difficulties of experimental methods to probe the microscopic dynamics, our understanding is still very limited.Among the well-established methods, e.g., transport measurements (30) or magnetic torque measurements (31, 32), photoemission measurements such as angle-resolved photoemission spectroscopy (ARPES) (33, 34) provide direct access to a material’s microscopic carrier distribution and dynamics. The interpretation of such ARPES measurement is, however, complicated by the interpretation of the bulk spectral function and the assumption of independent electron emission despite measuring a strongly correlated electronic state of matter. These are central questions to access the nature of the multibody state, which call for further developments and powerful new tools to aid in the interpretation of the physical mechanism.Therefore, the development of all-optical and ultrafast probes of the macroscopic dynamics inside such materials, which is compatible with existing methods, is highly desirable. To this aim, we apply HHS to investigate the transition between the different phases of the unconventional high-Tc superconductor YBa₂Cu₃O7−d (YBCO). We elucidate the connection between the measured optical spectra, the transition between strange metal and pseudogap phases, and the superconducting phase transition with a strong-field Hubbard model. The HHS measurement clearly shows a departure from the normal conducting phase with an increased formation of Cooper pairs upon cooling. The variation in harmonic orders is linked to phenomenological energy and phase relaxation times, which identify the transition to the fluctuation regime (35, 36), i.e., between the strange metal and pseudogap phases, and the sudden transition at Tc into the superconducting phase. Unconventional superconductors, like YBCO, are material systems in which the formation of composite bosons out of paired fermions is mediated not by phonon exchange but by some other kind of energy exchange (37), for instance, due to spin fluctuations. Such systems present many standing fascinating questions. It is thus important to have new powerful experimental techniques like HHS that provide a fresh and alternate view of the problem.     

Efficacy and safety of high dose versus low dose furosemide with or without dopamine infusion: The Dopamine in Acute Decompensated Heart Failure II (DAD-HF II) Trial

Aims

The role of low-dose dopamine infusion in patients with acute decompensated heart failure (ADHF) remains controversial. We aim to evaluate the efficacy and safety of high- versus low-dose furosemide with or without low-dose dopamine infusion in this patient population.

Methods and results

161 ADHF patients (78 years; 46% female; ejection fraction 31%) were randomized to 8-hour continuous infusions of: a) high-dose furosemide (HDF, n = 50, 20 mg/h), b) low-dose furosemide and low-dose dopamine (LDFD, n = 56, 5 mg/h and 5 μg kg^− 1 min^− 1 respectively), or c) low-dose furosemide (LDF, n = 55, furosemide 5 mg/h). The main outcomes were 60-day and one-year all-cause mortality (ACM) and hospitalization for HF (HHF). Dyspnea relief (Borg index), worsening renal function (WRF, rise in serum creatinine (sCr) ≥ 0.3 mg/dL), and length of stay (LOS) were also assessed. The urinary output at 2, 4, 6, 8, and 24 h was not significantly different in the three groups. Neither the ACM at day 60 (4.0%, 7.1%, and 7.2%; P = 0.74) or at one year (38.1%, 33.9% and 32.7%, P = 0.84) nor the HHF at day 60 (22.0%, 21.4%, and 14.5%, P = 0.55) or one year (60.0%, 50.0%, and 47%, P = 0.40) differed between HDF, LDFD, and LDF groups, respectively. No differences in the Borg index or LOS were noted. WRF was higher in the HDF than in LDFD and LDF groups at day 1 (24% vs. 11% vs. 7%, P < 0.0001) but not at sCr peak (44% vs. 38% vs. 29%, P = 0.27). No significant differences in adverse events were noted.

Conclusions

In ADHF patients, there were no significant differences in the in-hospital and post-discharge outcomes between high- vs. low-dose furosemide infusion; the addition of low-dose dopamine infusion was not associated with any beneficial effects.     

Adefovir plus lamivudine are more effective than adefovir alone in lamivudine-resistant HBeAg- chronic hepatitis B patients: A 4-year study

Background and Aim:  Adefovir dipivoxil (ADV) is effective in lamivudine (LAM)-resistant hepatitis B e antigen-negative (HBeAg^-) chronic hepatitis B (CHB). However, it is unclear whether LAM treatment should be continued in these patients. We aimed to compare the long-term efficacy of adding ADV to ongoing LAM treatment versus switching to ADV monotherapy in LAM-resistant HBeAg^- CHB.
Methods:  Sixty LAM-resistant patients with HBeAg^- CHB were randomly assigned (3:1) to combination therapy (10 mg ADV once daily plus ongoing LAM at 100 mg once daily [ n  = 45]) or 10 mg ADV monotherapy once daily ( n  = 15). Virological and biochemical responses were defined as hepatitis B virus (HBV)–DNA <400 copies/mL and as normalization of alanine aminotransferase levels, respectively.
Results:  The median follow-up time was 53 months (range 20–60 months). A virological response was observed in 38/45 (84.4%) and 11/15 (73.3%) patients in the ADV/LAM and ADV monotherapy groups, respectively ( P  = 0.56). Biochemical response rates were higher in the ADV/LAM group than in the ADV monotherapy group (90.9% vs 57.1%, respectively; P  = 0.01). In the ADV/LAM group, serum HBV–DNA remained undetectable in all patients who achieved a virological response ( n  = 38). In the ADV monotherapy group, virological breakthrough occurred in four of the 11 patients who achieved a virological response (36.4%; P  < 0.001 vs the ADV/LAM group, log–rank test). In addition, two patients in each group who did not achieve a virological response eventually developed ADV resistance.
Conclusions:  Adding ADV to LAM is more effective than switching to ADV monotherapy in LAM-resistant patients with HBeAg^- CHB.     

Evaluation of N-terminal prohormone B-type natriuretic Peptide in patients with acute coronary syndromes and percutaneous coronary intervention

The aim of this research was to describe N-terminal part of the prohormone B-type natriuretic peptide (NT-proBNP) levels over time in patients with acute coronary syndrome (ACS) before and after percutaneous coronary intervention (PCI). NT-proBNP, troponin I (Tn-I), creatine kinase (CK), CK MB isoenzyme (CKMB), fibrinogen, D-dimers, and C-reactive protein (CRP) were measured in 300 consecutive patients with ACS before undergoing successful reperfusion with PCI in the first 48 hours, 2 days after, and at the end of the 1st, 3rd, 6th, 12th, 18th, and 24th month. The concentration of NT-proBNP was cross-correlated with the levels of NT-proBNP in 300 patients without ACS and was significantly increased before and after PCI and at the end of the 3rd month, contrasting with the fast conversion to normal levels of Tn-I, CK, CKMB, fibrinogen, D-dimers, and CRP. In patients with ACS undergoing successful PCI, NT-proBNP shows slow kinetics, especially in patients with an increased thrombolysis in myocardial infarction risk score, hypertension, and diabetes. Nevertheless, cardiac neurohormonal activation may be a unifying feature among patients at high risk for cardiovascular events after ACS and PCI.     

Lamivudine/pegylated interferon alfa-2b sequential combination therapy compared with lamivudine monotherapy in HBeAg-negative chronic hepatitis B

BACKGROUND AND AIM: Monotherapy has been proven insufficient in achieving sustained control of chronic hepatitis B. We aimed to assess the efficacy of combined sequential administration of lamivudine and pegylated interferon alfa-2b in patients with hepatitis Be antigen (HBeAg)-negative chronic hepatitis B. METHODS: Eighteen patients were given sequential combination treatment starting with 3 months of lamivudine monotherapy followed by 9 months of pegylated interferon alfa-2b (after a 3-month period of concomitant administration of the two drugs) and 24 patients received lamivudine monotherapy. RESULTS: At the end of treatment, 88.9% of the patients who received sequential combination treatment and 70.8% of those who received lamivudine monotherapy had hepatitis B virus (HBV) DNA levels below 400 copies/mL (P = not significant). At the end of treatment, 72.2% of the patients who received sequential combination treatment and 70.8% of those who received lamivudine monotherapy achieved alanine aminotransferase normalization (P = not significant). After 12 months of follow up, 33.3% of the patients who received sequential combination treatment and 16.7% of those who received lamivudine monotherapy had HBV-DNA levels below 400 copies/mL (P = 0.4). After 12 months of follow up, 72.2% of the patients who received sequential combination treatment and 25.0% of those who received lamivudine monotherapy had normal alanine aminotransferase levels (P < 0.01). Twenty-five percent of the patients in the lamivudine monotherapy group had virological breakthrough compared to none in the sequential combination treatment group (P = 0.06). CONCLUSIONS: Sequential combination treatment is able to improve sustained biochemical response rates and prevent the emergence of lamivudine-resistant mutants in patients with HBeAg-negative chronic hepatitis B.