Not only people have memories, but also metals. Transition metal oxides (TMO) are extensively studied, technologically important materials, due to their complex electronic interactions – resulting in a large variety of collective phenomena. “Memory effects” in these oxides have aroused a huge amount of interest, being both of fundamental scientific interest and technological significance.
Dr. Amos Sharoni of Bar-Ilan University’s physics department and its Institute of Nanotechnology and Advanced Materials (BINA) has now uncovered a new kind of memory effect unrelated to those previously reported. Sharoni said the results of his work will have an important impact on additional research, both experimental and theoretical, and the simplicity of the experimental design will enable other groups studying relevant systems to perform similar measurements with ease.
Sharoni, together with his student Naor Vard, and supported by theoretical modeling by Yonatan Dubi of Ben-Gurion University in the Negev, used a simple experimental design to study changes in the properties of two TMOs, VO2 and NdNiO3, which undergo a metal-insulator phase-transition. Their results, just published in the journal Advanced Materials
, not only demonstrate a new phenomenon, but, importantly, also provide an explanation of its origin.
The multi-state nature of the memory effect, whereby more than one piece of information can coexist in the same space, could be harnessed for memory technology. And while deleted computer data is not secure and can be recovered – at least partially – by talented hackers, the “erase-upon-reading” property of this system could make an invaluable contribution to security technologies.
Metal-insulator transitions are transitions from a metal (material with good electrical conductivity of electric charges) to an insulator (material where conductivity of charges is quickly suppressed). These transitions can be achieved by a small variation of external parameters such as pressure or temperature.
In Sharoni’s experiment, the studied TMOs, when heated, transit from one state to another, and their properties undergo a change, beginning in a small area where “islands” develop and then grow, and vice-versa during cooling, similar to the coexistence of ice and water during melting. Sharoni cooled his samples while transition was in process, and then examined what happened when they were reheated. He found that when the reheated metal-oxide reached the temperature point at which re-cooling had occurred – that is, in the phase coexistence state – an increase in resistance was measured. This increase in resistance was observed at each different point at which cooling was initiated. This previously unknown and surprising phenomenon demonstrates the creation of a “memory.”
Sharoni likens the creation of a “scar” to the motion of waves on the seashore. A wave rushes up the beach and as it recedes it leaves a small sandy mound at the furthest point that it reached. When the wave returns, it slows and brakes as it reaches the mound obstacle in its path. However, if a strong wave follows, it rushes over the mound and destroys it. Similarly, Sharoni found that further heating the TMO enables it to complete transition and to cross the scarred boundaries, “healing” the scars and immediately erasing the memory. In contrast, cooling does not erase them.AGE GAP AFFECTS MARRIAGE SATISFACTION OVER TIME
Age gaps between husbands and wives – with the men usually older than their wives but in some cases, such as 64-year-old Brigitte Macron and her 39-yearold husband, French President Emmanuel Macron, the opposite is true – always arouse interest.
Men and women both report greater marital satisfaction with younger spouses, but that satisfaction fades over time in marriages with a significant age gap between the partners, according to new University of Colorado at Boulder research.
The findings, which were recently published online in the Journal of Population Economics
, examined 13 years’ worth of longitudinal data from over 7,600 Australian households. They suggested that marriages with large age gaps are less resilient in the face of economic downturns relative to their similarly-aged counterparts.
Unsurprisingly, the findings show that men reported greater marital satisfaction when paired with a younger spouse, especially in the early years of marriage, but the reverse appears to be true as well.
“We find that men who are married to younger wives are the most satisfied, and men who are married to older wives are the least satisfied,” said economics Prof. Terra McKinnish, a co-author of the new study.
“Women are also particularly dissatisfied when they’re married to older husbands and particularly satisfied if they’re married to younger husbands.” That initial satisfaction erodes rapidly, however, after six to 10 years of marriage for the couples with a big age gap between the partners.
“Over time, those who are married to a much older or younger spouse tend to have larger declines in marital satisfaction over time compared to those who are married to spouses who are similar in age,” said McKinnish.
One mechanism for this decline could be how the age difference between spouses affects the couple’s ability to respond to negative economic shocks, such as a job loss, McKinnish said.
“We looked at how couples respond to negative shocks, and in particular if they have a major bad economic shock or worsening of their household finances,” she said. “We find that when couples have a large age difference, they tend to have a much larger decline in marital satisfaction when faced with an economic shock than couples that have a very small age difference.”
A possible explanation for this, McKinnish said, is that similarly-aged couples are more in sync on life decisions that affect both partners (having children; general spending habits) and thus may be better equipped to adjust to a negative financial shock. By contrast, an unexpected financial shakeup could expose underlying tensions and mismatches in couples with a larger age gap.